MEDICAL    *SCH<S>©L 


COLLEGE  OF  PHARMACY 


_     COLLEGE  OF  P£- 

r<^      DEPARTMENT   '^ 

OF 

MATERIA  MEDICA 
to< 

OF 


HISTOLOGY  OF 
MEDICINAL   PLANTS 


BY 
WILLIAM  MANSFIELD,  A.M.,  PHAR.D. 

Professor  of  Histology  and   Pharmacognosy,   College  of 

Pharmacy  of  the  City  of  New  York 

Columbia  University 


TOTAL  ISSUE,   FOUR  THOUSAND 


NEW  YORK 
JOHN  WILEY  &  SONS,  INC. 

LONDON:    CHAPMAN    &    HALL,   LIMITED 


Copyright,  1916,  by 
WILLIAM  MANSFIELD 


9/20 


PREFACE . 

THE  object  of  the  book  is  to  provide  a  practical  scientific 
course  in  vegetable  histology  for  the  use  of  teachers  and  students 
in  schools  and  colleges. 

The  medicinal  plants  are  studied  in  great  detail  because 
they  constitute  one  of  the  most  important  groups  of  economic 
plants.  The  cells  found  in  these  plants  are  typical  of  the  cells 
occurring  in  the  vegetable  Idngdom ;  therefore  the  book  should 
prove  a  valuable  text-book  for  all  students  of  histology. 

The  book  contains  much  that  is  new.  In  Part  II,  which  is 
devoted  largely  to  the  study  of  cells  and  cell  contents,  is  a  new 
scientific,  yet  practical,  classification  of  cells  and  cell  contents. 
The  author  believes  that  his  classification  of  bast  fibres  and 
hairs  will  clear  up  much  of  the  confusion  that  students  have 
experienced  when  studying  these  structures. 

The  book  is  replete  with  illustrations,  all  of  which  are  from 
original  drawings  made  by  the  author.  As  most  of  these  illus- 
trations are  diagnostic  of  the  plants  in  which  they  occur,  they 
will  prove  especially  valuable  as  reference  plates. 

The  material  of  the  book  is  the  outgrowth  of  the  experience 
of  the  author  in  teaching  histology  at  the  College  of  Pharmacy 
of  the  City  of  New  York,  Columbia  University,  and  of  years 
of  practical  experience  gained  by  examining  powdered  drugs  in 
the  laboratory  of  a  large  importing  and  exporting  wholesale 
drug  house. 

The  author  is  indebted  to  Ernest  Leitz  and  Bausch  & 
Lomb  Optical  Company  for  the  use  of  cuts  of  microscopic 
apparatus  used  in  Part  I  of  the  book. 

The  author  also  desires  to  express  his  appreciation  to  Pro- 
fessor Walter  S.  Cameron,  who  has  rendered  him  much  valuable 

aid. 

WILLIAM  MANSFIELD. 

COLUMBIA  UNIVERSITY, 
September,  1916. 


CONTENTS 


PART  I 

SIMPLE   AND   COMPOUND   MICROSCOPES  AND  MICRO- 
SCOPIC TECHNIC 

CHAPTER  I 
THE  SIMPLE  MICROSCOPES 

PAGE 

Simple  microscopes,  forms  of 4 

CHAPTER  II 
COMPOUND  MICROSCOPES 

Compound  microscopes,  structure  of 7 

Compound  microscopes,  mechanical  parts  of 7 

Compound  microscopes,  optical  parts  of 9 

Compound  microscopes,  forms  of 12 

CHAPTER  III 
MICROSCOPIC  MEASUREMENTS 

Ocular  micrometer 19 

Stage  micrometer 19 

Mechanical  stage 21 

Micrometer  eye-pieces 21 

Camera  lucida 22 

Drawing  apparatus 23 

Microphotographic  apparatus 24 

CHAPTER  IV 

HOW  TO  USE  THE  MICROSCOPE 

Illumination 26 

Micro  lamp 27 

Care  of  the  microscope 28 

Preparation  of  specimens  for  cutting 28 

v 
I 


VI  CONTENTS 

:  U.I-. 

Paraffin  imbedding  oven     .                        30 

Paraffin  blocks 31 

Cutting  sections 31 

Hand  microtome 31 

Machine  microtomes 32 

CHAPTER  V 

REAGENTS 

Reagent  set 39 

Measuring  cylinder 40 

CHAPTER  VI 

HOW  TO  MOUNT  SPECIMENS 

Temporary  mounts 41 

Permanent  mounts 41 

Cover  glasses 43 

Glass  slides 44 

Forceps 45 

Needles 46 

Scissors 46 

Turntable 46 

Labeling 47 

Preservation  of  mounted  specimens 48 

Slide  box 48 

Slide  tray 48 

Slide  cabinet 49 


PART  II 

TISSUES,  CELLS  AND  CELL  CONTENTS 
CHAPTER  I 

THE  CELL 

Typical  cell  .  53 

Changes  in  a  cell  undergoing  division 55 

Origin  of  multicellular  plants 57 

CHAPTER  II 

THE  EPIDERMIS  AND  PERIDERM 

Leaf  epidermis 59 

Testa  epidermis 63 

Plant  hairs    .  66 


CONTENTS  Vll 

PAGE 

Forms  of  hairs 67 

Papillae 67 

Unicellular  hairs 69 

Multicellular  hairs 72 

Periderm 80 

Cork  periderm 80 

Stone  cell  periderm 85 

Parenchyma  and  stone  cell  periderm 85 

CHAPTER  III 

MECHANICAL  TISSUES 

Bast  fibres 89 

Crystal  bearing  bast  fibres 90 

Porous  and  striated  bast  fibres 92 

Porous  and  non-striated  bast  fibres 96 

Non-porous  and  striated  bast  fibres 96 

Non-porous  and  non-striated  bast  fibres        .                         96 

Occurrence  of  bast  fibres  in  powdered  drugs 103 

Wood  fibres 104 

Collenchyma  cells 106 

Stone  cells 109 

Endodermal  cells 116 

Hypodermal  cells 118 

CHAPTER  IV 

ABSORPTION  TISSUE 

Root  hairs 121 

CHAPTER  V 

CONDUCTING  TISSUE 

Vessels  and  tracheids 126 

Annular  vessels 127 

Spiral  vessels 127 

Sclariform  vessels 128 

Reticulate  vessels 131 

Pitted  vessels 131 

Pitted  vessels  with  bordered  pores 131 

Sieve  tubes 136 

Sieve  plate 138 

Medullary  bundles,  rays  and  cells 138 

Medullary  ray  bundle 139 

The  medullary  ray 139 

The  medullary  ray  cell 141 


Vlll  CONTENTS 

PAG! 

Structure  of  the  medullary  ray  cells 142 

Arrangement  of  the  medullary  ray  cells  in  the  medullary  ray       .      .      .  14: 

Latex  tubes 142 

Parenchyma .144 

Cortical  parenchyma 147 

Pith  parenchyma 147 

Leaf  parenchyma 150 

Aquatic  plant  parenchyma 150 

Wood  parenchyma ,  I5C 

Phloem  parenchyma I5C 

Palisade  parenchyma 150 


CHAPTER  VI 

AERATING  TISSUE 

Water  pores 151 

Stomata 151 

Relation  of  stomata  to  the  surrounding  cells 154 

Lenticels -  ...  157 

Intercellular  spaces 158 

CHAPTER  VII 

SYNTHETIC  TISSUE 

Photosynthetic  tissue 163 

Glandular  tissue 164 

Glandular  hairs 164 

Secretion  cavities 166 

Schizogenous  cavities 1 68 

Lysigenous  cavities 168 

Schizo-lysigenous  cavities 168 

CHAPTER  VIII 
STORAGE  TISSUE 

Storage  cells 173 

Storage  cavities 176 

Crystal  cavities 176 

Mucilage  cavities 176 

Latex  cavities 176 

Oil  cavity 178 

Glandular  hairs  as  storage  organs 178 

Storage  walls 179 


CONTENTS  IX 

i 

CHAPTER  IX 

CELL  CONTENTS 

PAGE 

Chlorophyll 182 

Leucoplastids 183 

Starch  grains 183 

Occurrence 184 

Outline 185 

Size 185 

Hilum 185 

Nature  of  hilum 188 

Inulin 194 

Mucilage 194 

Hesperidin 196 

Volatile  oil 196 

Tannin 196 

Aleurone  grains 197 

Structure  of  aleurone  grains 197 

Form  of  aleurone  grains               ^ 197 

Description  of  aleurone  grains 198 

Tests  for  aleurcne  grains 198 

Crystals 200 

Micro-crystals 200 

Raphides 200 

Rosette  crystals 202 

Solitary  crystals 205 

Cystoliths 210 

Forms  of  cystoliths 210 

Tests  for  cystoliths 215 


PART  III 

HISTOLOGY    OF    ROOTS,    RHIZOMES,    STEMS,    BARKS, 
WOODS,  FLOWERS,  FRUITS  AND  SEEDS 

CHAPTER  I 

ROOTS  AND  RHIZOMES 

Cross-section  of  pink  root 219 

Cross-section  of  ruellia  root 219 

Cross-section  of  spigelia  rhizome 223 

Cross-section  of  ruellia  rhizome 226 

Powdered  pink  root 227 

Powdered  ruellia  root 227 


X  CONTENTS 

CHAPTER  II 

STEMS 

PAGE 

Herbaceous  stems 233 

Cross-section,  spigelia  stem 233 

Ruellia  stem 235 

Powdered  horehound 237 

Powdered  spurious  horehound 237 

Insect  flower  stems 241 

CHAPTER  III 
WOODY  STEMS 

Buchu  stem .      .     242 

Mature  buchu  stem 242 

Powdered  buchu  stem 245 

CHAPTER  IV 

BARKS 

White  pine  bark 248 

Powdered  white  pine  bark 250 

CHAPTER  V 
WOODS 

Cross-section  quassia 254 

Radial-section  quassia 254 

Tangential-section  quassia        .  258 

CHAPTER  VI 

LEAVES 

Klip  buchu 260 

Powdered  klip  buchu 262 

Mountain  laurel 264 

Trailing  arbutus 264 

CHAPTER  VII 

FLOWERS 

Pollen  grains 270 

Non-spiny-walled  pollen  grains 273 

Spiny-walled  pollen  grains 273 

Stigma  papillae - 274 


CONTENTS                                        •  XI 

PAGE 

Powdered  insect  flowers      .      . .      .278 

Open  insect  flowers 280 

Powdered  white  daisies 282 

CHAPTER  VIII 

FRUITS 

Celery  fruit 285 

CHAPTER  IX 

SEEDS 

Sweet  almonds • .__ 289 

CHAPTER  X 
ARRANGEMENT  OF  VASCULAR  BUNDLES 

Types  of  fibro-vascular  bundles 292 

Radial  vascular  bundles 292 

Concentric  vascular  bundles 295 

Collateral  vascular  bundles 295 

Bi-collateral  vascular  bundles 298 

Open  collateral  vascular  bundles         298 


Part  I 

SIMPLE   AND    COMPOUND    MICROSCOPES 
AND    MICROSCOPIC   TECHNIC 


CHAPTER  I 
THE    SIMPLE    MICROSCOPES 

The  construction  and  use  of  the  simple  microscope  (magni- 
fiers) undoubtedly  date  back  to  very  early  times.  There  is 
sufficient  evidence  to  prove  that  spheres  of  glass  were  used  as 
burning  spheres  and  as  magnifiers  by  people  antedating  the 
Greeks  and  Romans. 

The  simple  microscopes  of  to-day  have  a  very  wide  range  of 
application  and  a  corresponding  variation  in  structure  and  in 
appearance. 

Simple  microscopes  are  used  daily  in  classifying  and  studying 
crude  drugs,  testing  linen  and  other  cloth,  repairing  watches, 
in  reading,  and  identifying  insects.  The  more  complex  simple 
microscopes  are  used  in  the  dissection  and  classification  of 
flowers. 

The  watchmaker's  loupe,  the  linen  tester,  the  reading  glass, 
the  engraver's  lens,  and  the  simplest  folding  magnifiers  consist 
of  a  double  convex  lens.  Such  a  lens  produces  an  erect,  en- 
larged image  of  the  object  viewed  when  the  lens  is  placed  so 
that  the  object  is  within  its  focal  distance.  The  focal  distance 
of  a  lens  varies  according  to  the  curvature  of  the  lens.  The 
greater  the  curvature,  the  shorter  the  focal  distance  and  the 
greater  the  magnification. 

The  more  complicated  simple  microscope  consists  of  two  or 
more  lenses.  The  double  and  triple  magnifiers  consist  of  two 
and  three  lenses  respectively. 

When  an  object  is  viewed  through  three  lenses,  the  magnifi- 
cation is  greater  than  when  viewed  through  one  or  two  lenses, 
but  a  smaller  part  of  the  object  is  magnified. 

3 


4  HISTOLOGY   OF  MEDICINAL  PLANTS 

FORMS  OF  SIMPLE  MICROSCOPES 

TRIPOD    MAGNIFIER 

The  tripod  magnifier  (Fig.  i)  is  a  simple  lens  mounted  on  a 
mechanical  stand.  The  tripod  is  placed  over  the  object  and 
the  focus  is  obtained  by  means  of  a  screw  which  raises  or  lowers 
the  lens,  according  to  the  degree  it  is  magnified. 

WATCHMAKER'S  LOUPE 

The  watchmaker's  loupe  (Fig.  2)  is  a  one-lens  magnifier 
mounted  on  an  ebony  or  metallic  tapering  rim,  which  can  be 


FIG.  i.— Tripod  Magnifier  FIG.  2.— Watchmaker's  Loupe 

placed  over  the  eye  and  held  in  position  by  frowning  or  con- 
tracting the  eyelid. 

FOLDING    MAGNIFIER 

The  folding  magnifier  (Fig.  3)  of  one  or  more  lenses  is  mounted 
in  such  a  way  that,  when  not  in  use,  the  lenses  fold  up  like  the 


FIG.  3. — Folding  Magnifier  FIG.  4. — Reading  Glass 

blade  of  a  knife,  and  when  so  folded  are  effectively  protected 
from  abrasion  by  the  upper  and  lower  surfaces  of  the  folder. 


READING    GLASSES 


Reading  glasses  (Fig.  4)  are  large  simple  magnifiers,  often 
six  inches  in  diameter.  The  lens  is  encircled  with  a  metal  band 
and  provided  with  a  handle. 


THE   SIMPLE  MICROSCOPES 
STEINHEIL   APLANATIC    LENSES 


Steinheil  aplanatic  lenses  (Fig.  5)  consist  of  three  or  four 
lenses  cemented  together.  The  combination  is  such  that  the 
field  is  large,  flat,  and  achromatic.  These  lenses  are  suitable 


FlG.  5. — Steinheil  Aplanatic  Lens 

for  field,   dissecting,   and  pocket  use.     When  such  lenses  are 
placed  in  simple  holders,  they  make  good  dissecting  microscopes. 


DISSECTING   MICROSCOPE 


The  dissecting  microscope  (Fig.  6)  consists  of  a  Steinheil 
lens  and  an  elaborate  stand,  a  firm  base,  a  pillar,  a  rack  and 


FIG.  6. — Dissecting  Microscope 


6  HISTOLOGY   OF  MEDICINAL  PLANTS 

pinion,  a  glass  stage,  beneath  which  there  is  a  groove  for  holding 
a  metal  plate  with  one  black  and  one  white  surface.  The 
nature  of  the  object  under  observation  determines  whether  a 
plate  is  used.  When  the  plate  is  used  and  when  the  object  is 
studied  by  reflected  light  it  is  sometimes  desirable  to  use  the 
black  and  sometimes  the  white  surface.  The  mirror,  which  has 
a  concave  and  a  plain  surface,  is  used  to  reflect  the  light  on  the 
glass  stage  when  the  object  is  studied  by  transmitted  light. 
The  dissecting  microscope  magnifies  objects  up  to  twenty 
diameters,  or  twenty  times  their  real  size. 


CHAPTER  II 
COMPOUND   MICROSCOPES 

The  compound  microscope  has  undergone  wonderful  changes 
since  1667,  the  days  of  Robert  Hooke.  When  we  consider  the 
crude  construction  and  the  limitations  of  Robert  Hooke's  micro- 
scope, we  marvel  at  the  structural  perfection  and  the  unlimited 
possibilities  of  the  modern  instrument.  The  advancement  made 
in  most  sciences  has  followed  the  gradual  perfection  of  this 
instrument. 

The  illustration  of  Robert  Hooke's  microscope  (Fig.  7)  will 
convey  to  the  mind  more  eloquently  than  words  the  crudeness 
of  the  early  microscopes,  especially  when  it  is  compared  with 
the  present-day  microscopes. 

STRUCTURE  OF  THE  COMPOUND  MICROSCOPE 

The  parts  of  the  compound  microscope  (Fig.  8)  may  be 
grouped  into — first,  the  mechanical,  and,  secondly,  into  the 
optical  parts. 

THE    MECHANICAL    PARTS 

1.  The  foot  is  the  basal  part,  the  part  which  supports  all 
the  other  mechanical  and  optical  parts.     The  foot  should  be 
heavy  enough  to  balance  the  other  parts  when  they  are  inclined. 
Most    modern    instruments    have    a    three-parted    or    tripod- 
shaped  base. 

2.  The  pillar  is  the  vertical  part  of  the  microscope  attached 
to  the  base.     The  pillar  is  joined  to  the  limb  by  a  hinged  joint. 
The  hinges  make  it  possible  to  incline  the  microscope  at  any 
angle,  thus  lowering  its  height.     In  this  way,  short,  medium, 
and  tall   persons  can  use   the   microscope  with   facility.     The 
part  of  the  pillar  above  the  hinge  is  called  the  limb.     The  limb 
may  be  either  straight  or  curved.     The  curved  form  is  pref- 
erable, since  it  offers  a  more  suitable  surface  to  grasp  in  trans- 
ferring from  box  or  shelf  to  the  desk,  and  vice  versa. 

7 


8 


HISTOLOGY   OF   MEDICINAL  PLANTS 


FIG.  7. — Compound  Microscope  of  Robert  Hooke 


COMPOUND  MICROSCOPES  9 

3.  The   stage   is  either  stationary  or  movable,   round  or 
square,  and  is  attached  to  the  limb  just  above  the  hinge.     The 
upper  surface  is  made  of  a  composition  which  is  not  easily 
attacked  by  moisture  and  reagents.     The  centre  of  the  stage  is 
perforated  by  a  circular  opening. 

4.  The  sub-stage  is  attached  below  the  stage  and  is  for  the 
purpose   of  holding   the  iris  diaphragm  and  Abbe  condenser. 
The  raising  and  lowering  of  the  sub-stage  are  accomplished  by 
a  rack  and  pinion. 

5.  The  iris  diaphragm,  which  is  held  in  the  sub-stage  below 
the  Abbe  condenser,  consists  of  a  series  of  metal  plates,  so  ar- 
ranged that  the  light  entering  the  microscope  may  be  cut  off 
completely  or  its  amount  regulated  by  moving  a  control  pin. 

6.  The  fine  adjustment  is  located  either  at  the  side  or  at 
the  top  of  the  limb.     It  consists  of  a  fine  rack  and  pinion,  and 
is  used  in  focusing  an  object  when  the  low-power  objective  is  in 
position,  or  in  finding  and  focusing  the  object  when  the  high- 
power  objective  is  in  position. 

7.  The  coarse  adjustment  is  a  rack  and  pinion  used  in  raising 
and  lowering  the  body-tube  and  in  finding  the  approximate 
focus  when  either  the  high-  or  low-power  objective  is  in  position. 

8.  The  body-tube  is  the  path  traveled  by  the  rays  of  light 
entering  the  objectives  and  leaving  by  the  eye-piece.     To  the 
lower  part  of  the  tube  is  attached  the  nose-piece,  and  resting 
in  its  upper  part  is  the  draw-tube,  which  holds  the  eye-piece. 
On  the  outer  surface  of  the  draw-tube  there  is  a  scale  which 
indicates  the  distance  it  is  drawn  from  the  body-tube. 

9.  The  nose-piece  may  be  simple,  double,  or  triple,  and  it 
is  protected  from  dust  by  a  circular  piece  of  metal.     Double  and 
triple  nose-pieces  may  be  revolved,  and  like  the  simple  nose- 
piece  they  hold  the  objectives  in  position. 

THE   OPTICAL  PARTS 

i .  The  mirror  is  a  sub-stage  attachment  one  surface  of  which 
is  plain  and  the  other  concave.  The  plain  surface  is  used  with 
an  Abbe  condenser  when  the  source  of  light  is  distant,  while 
the  concave  surface  is  used  with  instruments  without  an  Abbe 
condenser  when  the  source  of  light  is  near  at  hand. 


10 


HISTOLOGY   OF  MEDICINAL   PLANTS 


epiece 


Body  Tube 


Coarse 
Adjustment 


Revolving  Nosep 
for  three  Objectives 


Stage 


ne  Adjustment 


•Limb 


FIG.  8. — Compound  Microscope 


COMPOUND   MICROSCOPES 


11 


2.  The  Abbe  condenser  (Fig.  9)  is  a  combination  of  two  or 
more  lenses,  arranged  so  as  to  concentrate  the  light  on  the 
specimen  placed  on  the  stage.     The  condenser  is  located  in  the 
opening   of   the   stage,  and   its  uppermost 

surface  is  circular  and  flat. 

3.  Objectives   (Figs.    10,    n,    and    12). 
There    are  low,    medium,    and   high-power 
objectives.     The  low-power  objectives  have 
fewer  and  larger  lenses,  and  they  magnify 
least,  but  they  show  more  of  the  object  than 
do  the  high-power  objectives. 

There    are  three    chief  types  of   objec- 
tives:    First,  dry    objectives;    second,  wet 
objectives,   of   which    there    are    the    water-immersion    objec- 
tives;   and    third,    the    oil-immersion    objectives.      The     dry 
objectives    are    used   for    most    histological    and    pharmacog- 
nostical   work.      For   studying   smaller   objects  the  water  ob- 


FIG.  9.— Abbe 
Condenser 


FIG.  10. 


FIG.  ii. 
Objectives. 


FIG.  12. 


jective  is  sometimes  desirable,  but  in  bacteriological  work  the 
oil-immersion  objective  is  almost  exclusively  used.  The  globule 
of  water  or  oil,  as  the  case  may  be,  increases  the  amount  of  light 
entering  the  objective,  because  the  oil  and  water  bend  many 
rays  into  the  objective  which  would  otherwise  escape. 

4.  Eye-pieces  (Figs.  13,  14,  and  15)  are  of  variable  length, 
but  structurally  they  are  somewhat  similar.  The  eye-piece 
consists  of  a  metal  tube  with  a  blackened  inner  tube.  In  the 


12 


HISTOLOGY   OF   MEDICINAL   PLANTS 


centre  of  this  tube  there  is  a  small  diaphragm  for  holding  the 
ocular  micrometer.  In  the  lower  end  of  the  tube  a  lens  is  fas- 
tened by  means  of  a  screw.  This,  the  field  lens,  is  the  larger 
lens  of  the  ocular.  The  upper,  smaller  lens  is  fastened  in  the 


FIG.  13. 


FIG.  14. 
Eye-Pieces. 


FIG.  15. 


tube  by  a  screw,  but  there  is  a  projecting  collar  which  rests, 
when  in  position,  on  the  draw-tube. 

The  longer  the  tube  the  lower  the  magnification.  For 
instance,  a  two-inch  ocular  magnifies  less  than  an  inch  and  a 
half,  a  one-inch  less  than  a  three-fourths  of  an  inch,  etc. 

The  greater  the  curvature  of  the 
lenses  of  the  ocular  the  higher  will  be 
the  magnification  and  the  shorter  the 
tube-length. 

FORMS   OF   COMPOUND 
MICROSCOPES 

The  following  descriptions  refer  to 
three  different  models  of  compound 
microscopes:  one  which  is  used  chiefly 
as  a  pharmacognostic  microscope,  one 
as  a  research  microscope  stand,  while 
the  third  type  represents  a  research 
microscope  stand  of  highest  order, 
which  is  used  at  the  same  time  for 
taking  microphotographs. 

PHARMACOGNOSTIC  MICROSCOPE 

FIG.  i6.-Pharmacognostic          The    pharmacognostic    microscope 
Microscope  (Fig.    1 6)    is     an     instrument    which 


COMPOUND  MICROSCOPES  13 

embodies  only  those  parts  which  are  most  essential  for  the 
examination  of  powdered  drugs,  bacteria,  and  urinary 
sediments.  This  microscope  is  provided  with  a  stage  of  the 
dimensions  105  x  105  mm.  This  factor  and  the  distance  of 
80  mm.  from  the  optical  centre  to  the  handle  arm  render  it 
available  for  the  examination  of  even  very  large  objects  and 
preparations,  or  preparations  suspended  in  glass  dishes.  The 
stand  is  furnished  with  a  side  micrometer,  a  fine  adjustment 
having  knobs  on  both  sides,  thereby  permitting  the  manipula- 
tion of  the  micrometer  screw  either  by  left  or  right  hand.  The 
illuminating  apparatus  consists  of  the  Abbe  condenser  of  numeri- 
cal aperture  of  1.20,  to  which  is  attached  an  iris -diaphragm  for 
the  proper  adjustment  of  the  light.  A  worm  screw,  mounted 
in  connection  with  the  condenser,  serves  for  the  raising  and 
lowering  of  the  condenser,  so  that  the  cone  of  illuminating 
pencils  can  be  arranged  in  accordance  to  the  objective  employed 
and  to  the  preparation  under  observation.  The  objectives 
necessary  are  those  of  the  achromatic  type,  possessing  a  focal 
length  of  1 6. 2  mm.  and  3  mm.  Oculars  which  render  the  best 
results  in  regard  to  magnification  in  connection  with  the  two 
objectives  mentioned  are  the  Huyghenian  eye-pieces  II  and  IV 
so  that  magnifications  are  obtained  varying  from  62  to  625. 
It  is  advisable,  however,  to  have  the  microscope  equipped  with 
a  triple  revolving  nose-piece  for  the  objectives,  so  that  provision 
is  made  for  the  addition  of  an  oil-immersion  objective  at  any 
time  later  should  the  microscope  become  available  for  bac- 
teriological investigations. 

THE  RESEARCH  MICROSCOPE 

The  research  microscope  used  in  research  work  (Fig.  1 7)  must 
be  equipped  more  elaborately  than  the  microscope  especially 
designed  for  the  use  of  the  pharmacognosist.  While  the  simple 
form  of  microscope  is  supplied  with  the  small  type  of  Abbe 
condenser,  the  research  microscope  is  furnished  with  a  large 
illuminating  apparatus  of  which  the  iris  diaphragm  is  mounted 
on  a  rack  and  pinion,  allowing  displacement  obliquely  to  the 
optical  centre,  also  to  increase  resolving  power  in  the  objectives 
when  observing  those  objects  which  cannot  be  revealed  to  the 
best  advantage  with  central  illumination.  Another  iris  is 


14 


HISTOLOGY   OF  MEDICINAL  PLANTS 


furnished  above  the  condenser;  this  iris  becomes  available  the 
instant  an  object  is  to  be  observed  without  the  aid  of  the  con- 
denser, in  which  case  the  upper  iris  diaphragm  allows  proper 
adjustment  of  the  light.  The  mirror,  one  side  plane,  the  other 
concave,  is  mounted  on  a  movable  bar,  along  which  it  can 
be  slid — another  convenience  for  the  adjustment  of  the  light. 
The  microscope  stage  of  this  stand  is  of  the  round,  rotating 


FIG.  17. — Research 
Microscope 


FIG.  1 8. — Special 
Research  Microscope 


and  centring  pattern,  which  permits  a  limited  motion  to  the 
object  slide:  The  rotation  of  the  microscope  stage  furnishes 
another  convenience  in  the  examination  of  objects  in  polarized 
light,  allowing  the  preparation  to  be  rotated  in  order  to 
distinguish  the  polarization  properties  of  the  objects  under 
observation. 

SPECIAL  RESEARCH  MICROSCOPE 

A  special  research  microscope  of  the  highest  order  (Fig.  18) 
is  supplied  with  an  extra  large  body  tube,  which  renders  it  of 


COMPOUND  MICROSCOPES 


15 


special  advantage  for  micro-photography.  Otherwise  in  its 
mechanical  equipment  it  resembles  very  closely  the  medium- 
sized  research  microscope  stand,  with  the  exception  that  the 
stand  is  larger  in  its  design,  therefore  offering  universal  applica- 
tion. In  regard  to  the  illuminating  apparatus,  it  is  advisable 
to  mention  that  the  one  in  the  large  research  microscope  stand 
is  furnished,  with  a  three-lens  condenser  of  a  numerical  aperture 
of  1.40,  while  the  medium-sized  research  stand  is  provided  with 
a  two-lens  condenser  of  a  numerical  aperture  of  1.20.  The 
stage  of  the  microscope  is  provided  with  a  cross  motion — the 
backward  and  forward  motion  of  the  preparation  is  secured  by 
rack  and  pinion,  while  the  side  motion 
is  controlled  by  a  micrometric  worm 
screw.  In  cases  where  large  prepa- 
rations are  to  be  photographed,  the 
draw-tube  with  ocular  and  the  slider 
hi  which  the  draw-tubes  glide  are 
removed  to  allow  the  full  aperture 
of  wide-angle  objectives  to  be  made 
use  of. 

BINOCULAR  MICROSCOPE 

The  Gre enough  binocular  micro- 
scope, as  shown  in  Fig.  19,  consists 
of  a  microscope  stage  with  two  tubes 
mounted  side  by  side  and  moving  on 
the  same  rack  and  pinion  for  the 
focusing  adjustment.  Either  tube 
can  be  used  without  the  other.  The 
oculars  are  capable  of  more  or  less 
separation  to  suit  the  eyes  of  different 
observers.  In  each  of  the  drub-like 
mountings,  near  the  point  where  the 
oculars  are  introduced,  porro-prisms 

have  been  placed,  which  erect  the  image.  This  microscope 
gives  most  perfect  stereoscopic  images,  which  are  erect  instead 
of  inverted,  as  in  the  monocular  compound  microscopes.  The 
Greenough  binocular  microscope  is  especially  adapted  for  dis- 
section and  for  studying  objects  of  considerable  thickness. 


FIG.  19. — Greenough 
Binocular  Microscope 


16 


HISTOLOGY   OF  MEDICINAL  PLANTS 


.POLARIZATION  MICROSCOPE 

The  polarization  microscope  (Fig.  20)  is  used  chiefly  for  the 
examination  of  crystals  and  mineral  sections  as  well  as  for  the 
observation  of  organic  bodies  in  polarized  light.  It  can,  how- 
ever, also  be  used  for  the  examination  of  regular  biological 
preparations. 

If  compared  with  the  regular  biological  microscope,  the 
polarization  microscope  is  found  characteristic  of  the  following 
points:  it  is  supplied  with  a  polarization  arrangement.  The 
latter  consists  of  a  polarizer  and  analyzer.  The  polarizer  is 
situated  in  a  rotating  mount  beneath  the  condensing  system. 
The  microscope,  of  which  the  diagram  is 
shown,  possesses  a  triple  "Ahrens"  prism 
of  calcite.  The  entering  light  is  divided 
into  two  polarized  parts,  situated  perpen- 
dicularly to  each  other.  The  so-called 
"ordinary"  rays  are  reflected  to  one  side 
by  total  reflection,  which  takes  place  on 
the  inner  cemented  surface  of  the  triple 
prism,  allowing  the  so-called  "extra- 
ordinary" rays  to  pass  through  the  con- 
denser. If  the  prism  is  adjusted  to  its 
focal  point,  it  is  so  situated  that  the 
vibration  plane  of  the  extra-ordinary  rays 
are  in  the  same  position  as  shown  in 
the  diagram  of  the  illustration. 

The  analyzer  is  mounted  within  the 
microscope-tube     above     the    objective. 

Situated  on  a  sliding  plate,  it  can  be  shifted  into  the  optical 
axis  whenever  necessary.  The  analyzer  consists  of  a  polari- 
zation prism  after  Glan-Thompson.  The  polarization  plane 
of  the  active  extraordinary  rays  is  situated  perpendicularly 
to  the  plane  as  shown  in  the  diagram.  The  polarization 
prisms  are  ordinarily  crossed.  In  this  position  the  field  of 
the  microscope  is  darkened  as  long  as  no  substance  of  a  double 
refractive  index  has  been  introduced  between  the  analyzer  and 
polarizer.  In  rotating  the  polarizer  up  to  the  mark  90,  the 
polarization  prisms  are  mounted  parallel  and  the  field  of  the 


FIG.  20. — Polarization 
Microscope 


COMPOUND  MICROSCOPES  17 

microscope  is  lighted  again.  Immediately  above  the  analyzer 
and  attached  to  the  mounting  of  the  analyzer  a  lens  of  a  com- 
paratively long  focal  length  has  been  placed  in  order  to  over- 
come the  difference  in  focus  created  by  the  introduction  of  the 
analyzer  into  the  optical  rays. 

The  condensing  system  is  mounted  on  a  slider,  and,  further- 
more, can  be  raised  and  lowered  along  the  optical  centre  by 
means  of  a  rack-and-pinion  adjustment.  If  lowered  sufficiently, 
the  condensing  system  can  be  thrown  to  the  side  to  be  removed 
from  the  optical  rays.  The  condenser  consists  of  three  lenses. 
The  two  upper  lenses  are  separately  mounted  to  an  arm,  which 
permits  them  to  be  tilted  to  one  side  in  order  to  be  removed 
from  the  optical  rays.  The  complete  condenser  is  used  only 
in  connection  with  high-power  objectives.  As  far  as  low-power 
objectives  are  concerned,  the  lower  condensing  lens  alone  is 
made  use  of,  and  the  latter  is  found  mounted  to  the  polarizer 
sleeve.  Below  the  polarizer  and  above  the  lower  condensing 
lens  an  iris  diaphragm  is  found. 

The  microscope  table  is  graduated  on  its  periphery,  and, 
furthermore,  carries  a  vernier  for  more  exact  reading. 

The  polarization  microscope  is  not  furnished  with  an  ob- 
jective nose-piece.  Every  objective,  however,  is  supplied  with 
an  individual  centring  head,  which  permits  the  objective  to  be 
attached  to  an  objective  clutch-changer,  situated  at  the  lower  end 
of  the  microscope-tube.  The  centring  head  permits  the  objectives 
to  be  perfectly  centred  and  to  remain  centred  even  if  another 
objective  is  introduced  into  the  objective  clutch-changer. 

At  an  angle  of  45  degrees  to  the  polarization  plane  of  polarizer 
and  analyzer,  a  slot  has  been  provided,  which  serves  for  the 
introduction  of  compensators. 

Between  analyzer  and  ocular,  another  slot  is  found  which 
permits  the  Amici-Bertrand  lens  to  be  introduced  into  the 
optical  axis.  The  slider  for  the  Bertrand  lens  is  supplied  with 
two  centring  screws  whereby  this  lens  can  be  perfectly  and 
easily  centred.  The  Bertrand  lens  serves  the  purpose  of 
observing  the  back  focal  plane  of  the  microscope  objective.  In 
order  to  allow  the  Bertrand  lens  to  be  focused,  the  tube  can  be 
raised  and  lowered  for  this  purpose.  An  iris  diaphragm  is 
mounted  above  the  Bertrand  lens. 


18  HISTOLOGY   OF   MEDICINAL   PLANTS 

If  the  Bcrtrand  lens  is  shifted  out  of  the  optical  axis,  one  can 
observe  the  preparation  placed  upon  the  microscope  stage  and, 
depending  on  its  thickness  or  its  double  refraction,  the  inter- 
ference color  of  the  specimen.  This  interference  figure  is  called 
the  orthoscopic  image  and,  accordingly,  one  speaks  of  the  micro- 
scope as  being  used  as  an  "orthoscope." 

After  the  Bertrand  lens  has  been  introduced  into  the  optical 
axis,  the  interference  figure  is  visible  in  the  back  focal  plane  of 
the  objective.  Each  point  of  this  interference  figure  corresponds 
to  a  certain  direction  of  the  rays  of  the  preparation  itself.  This 
arrangement  permits  observation  of  the  change  of  the  reflection 
of  light  taking  place  in  the  preparation,  this  in  accordance  with 
the  change  of  the  direction  of  the  rays.  This  interference  figure 
is  called  the  conoscopic  image,  and,  accordingly,  the  microscope 
is  used  as  a  "conpscope." 

Many  types  of  polarization  microscopes  have  been  con- 
structed; those  of  a  more  elaborate  form  are  used  for  research 
investigations;  others  of  smaller  design  for  routine  investigations. 


CHAPTER  III 
MICROSCOPIC  MEASUREMENTS 

In  making  critical  examinations  of  powdered  drugs,  it  is 
frequently  necessary  to  measure  the  elements  under  observation, 
particularly  in  the  case  of  starches  and  crystals. 

OCULAR  MICROMETER 

Microscopic  measurements  are  made  by  the  ocular  microm- 
eter (Fig.  21).  This  consists  of  a  circular  piece  of  transparent 
glass  on  the  centre  of  which  is  etched  a  one-  or  two-millimeter 
scale  divided  into  one  hundred  or  two  hundred  divisions  re- 


FlG.  21. — Ocular  Micrometer  FIG.  22. — Stage  Micrometer 

spectively.     The  value  of  each  line  is  determined  by  standard- 
izing with  a  stage  micrometer. 

STAGE   MICROMETER 

The -stage  micrometer  (Fig.  22)  consists  of  a  glass  slide  upon 
which  is  etched  a  millimeter  scale  divided  into  one  hundred 
equal  parts  or  lines:  each  line  has  a  value  of  one  hundredth  of 
a  millimeter. 

STANDARDIZATION    OF    OCULAR     MICROMETER    WITH     LOW-POWER 

OBJECTIVE 

Having  placed  the  ocular  micrometer  in  the  eye-piece  and 
the  stage  micrometer  on  the  centre  of  the  stage,  focus  until 

19 


20  HISTOLOGY   OF  MEDICINAL  PLANTS 

the  lines  of  the  stage  micrometer  are  clearly  seen.  Then  adjust 
the  scales  until  the  lines  of  the  stage  micrometer  are  parallel 
with  and  directly  under  the  lines  of  the  ocular  micrometer. 

Ascertain  the  number  of  lines  of  the  stage  micrometer  covered 
by  the  one  hundred  lines  of  the  ocular  micrometer.  Then 
calculate  the  value  of  each  line  of  the  ocular.  This  is  done  in 
the  following  manner: 

If  the  one  hundred  lines  of  the  ocular  cover  seventy-five 
lines  of  the  stage  micrometer,  then  the  one  hundred  lines  of 
the  ocular  micrometer  are  equivalent  to  seventy-five  one- 
hundredths,  or  three-fourths,  of  a  millimeter.  One  line  of  the 
ocular  micrometer  will  therefore  be  equivalent  to  one-hundredth 


FIG.  23. — Micrometer  Eye- Piece 

of  seventy-five  one-hundredths,  or  .0075  part  of  a  millimeter, 
and  as  a  micron  is  the  unit  for  measuring  microscopic  objects, 
this  being  equivalent  to  one  one-thousandth  of  a  millimeter, 
the  value  of  each  line  of  the  ocular  will  therefore  be  7.5  microns. 

With  the  high-power  objective  in  place,  ascertain  the  value 
of  each  line  of  the  ocular.  If  one  hundred  lines  of  the  ocular 
cover  only  twelve  lines  of  the  stage  micrometer,  then  the  one 
hundred  lines  of  the  ocular  are  equivalent  to  twelve  one-hun- 
dredths of  a  millimeter,  the  value  of  one  line  being  equivalent 
to  one  one-hundredth  of  twelve  one-hundredths,  or  twelve  ten- 
thousandths  of  a  millimeter,  or  .0012,  or  1.2  u. 

It  will  therefore  be  seen  that  objects  as  small  as  a  thousandth 
of  a  millimeter  can  be  accurately  measured  by  the  ocular 
micrometer. 

In  making  microscopic  measurements  it  is  only  necessary 


MICROSCOPIC  MEASUREMENTS 


21 


to  find  how  many  lines  of  the  ocular  scale  are  covered  by  the 
object.  The  number  of  lines  multiplied  by  the  equivalent  of 
each  line  will  be  the  size  of  the  object  in  microns,  or  micro- 
millimeters. 

MICROMETER  EYE-PIECES 

Micrometer  eye-pieces  (Figs.  23  and  24)  may  be  used  in 
making  measurements.    These  eye-pieces  with  micrometer  com- 


FIG.  24. — Micrometer  Eye- Piece 

binations  are  preferred  by  some  workers,  but  the  ocular  microm- 
eter will  meet  the  needs  of  the  average  worker. 

MECHANICAL  STAGES 

Moving  objects  by  hand  is  tiresome  and  unsatisfactory,  first, 
because  of  the  possibility  of  losing  sight  of  the  object  under 
observation,  and  secondly,  because  the  field  cannot  be  covered 
so  systematically  as  when  a  mechanical  stage  is  used  for  moving 
slides. 

The  mechanical  stage  (Fig.  25)  is  fastened  to  the  stage  by 
a  screw.  The  slide  is  held  by  two  clamps.  There  is  a  rack  and 


22 


HISTOLOGY   OF   MEDICINAL  PLANTS 


pinion  for- moving  the  slide  to  left  or  right,  and  another  rack  and 
pinion  for  moving  the  slide  forward  and  backward. 

CAMERA   LUCIDA 

The  camera  lucida  is  an  optical  mechanical  device  for  aiding 
the  worker  in  making  drawings  of  microscopic  objects.     The 


FIG.  27. 


'amera  Lucicia 


instrument  is  particularly  necessary  in  research  work  where  it 
is  desirable  to  reproduce  an  object  in  all  its  details.  In  fact,  all 
reproductions  illustrating  original  work  should  be  made  by 
means  of  the  camera  lucida  or  by  microphotography. 

A  great  many  different  types  of  camera  lucidas  or  drawing 
apparatus  are  obtainable,  varying  from  simple-inexpensive  to 
complex-expensive  forms.  Figs.  26,  27,  and  28  show  simple 
and  complex  forms. 


HISTOLOGY   OF  MEDICINAL  PLANTS 


MICROPHOTOGRAPHIC  APPARATUS 

The  microphotographic  apparatus  (Fig.  29),  as  the  name 
implies,  is  an  apparatus  constructed  in  such  a  manner  that  it 
may  be  attached  to  a  microscope  when  we  desire  to  photograph 
microscopic  objects.  It  consists  of  a  metal  base  and  a  polished 
metal  pillar  for  holding  the  bellows,  slide  holder,  ground-glass 
observation  plate,  and  eye-piece.  In  making  photographs,  the 
small  end  of  the  bellows  is  attached  to  the  ocular  of  the  micro- 


FlG.  29. — Microphotographic  Apparatus 


scope,  the  locus  adjusted,  and  the  object  or  objects  photo- 
graphed. More  uniform  results  are  obtained  in  making  such 
photographs  if  an  artificial  light  of  an  unvarying  candle-power 
is  used. 

There  are  obtainable  more  elaborate  microphotographic 
apparatus  than  the  one  figured  and  described,  but  for  most 
workers  this  one  will  prove  highly  satisfactory.  It  is  possible, 
by  inclining  the  tube  of  the  microscope,  to  make  good  micro- 
photographs  with  an  ordinary  plate  camera.  This  is  accom- 
plished by  removing  the  lens  of  the  camera  and  attaching  the 
bellows  to  the  ocular,  focusing,  and  photographing. 


CHAPTER  IV 

HOW  TO  USE  THE  MICROSCOPE 

In  beginning  work  with  the  compound  microscope,  place 
the  base  of  the  microscope  opposite  your  right  shoulder,  if  you 
are  right-handed;  or  opposite  your  left  shoulder,  if  you  are  left- 
handed.  Incline  the  body  so  that  the  ocular  is  on  a  level  with 
your  eye,  if  necessary;  but  if  not,  work  with  the  body  of  the 
microscope  in  an  erect  position.  In  viewing  the  specimen,  keep 
both  eyes  open.  Use  one  eye  for  observation  and  the  other 
for  sketching.  In  this  way  it  will  not  be  necessary  to  remove 
the  observation  eye  from  the  ocular  unless  it  be  to  complete 
the  details  of  a  sketch. 

Learn  to  use  both  eyes.  Most  workers,  however,  accustom 
themselves  to  using  one  eye;  when  they  are  sketching,  they  use 
both  eyes,  although  it  is  not  necessary  to  do  so. 

Open  the  iris  diaphragm,  and  incline  the  mirror  so  that 
white  light  is  reflected  on  the  Abb6  condenser.  Place  the  slide 
on  the  centre  of  the  stage,  and  if  the  slide  contains  a  section 
of  a  plant,  move  the  slide  so  as  to  place  this  specimen  over  the 
centre  of  the  Abbe  condenser.  Then  lower  the  body  by  means 
of  the  coarse  adjustment  until  the  low-power  object,  which 
should  always  be  in  position  when  work  is  begun,  is  within  one- 
fourth  of  an  inch  of  the  stage.  Then  raise  the  body  by  means 
of  the  coarse  adjustment  until  the  object,  or  objects,  in  case  a 
powder  is  being  examined,  is  seen.  Open  and  close  the  iris 
diaphragm,  finally  adjusting  the  opening  so  that  the  best  pos- 
sible illumination  is  obtained  for  bringing  out  clearly  the  struc- 
ture of  the  object  or  objects  viewed.  Then  regulate  the  focus 
by  moving  the  body  up  or  down  by  turning  the  fine  adjustment. 
When  studying  cross-sections  or  large  particles  of  powders,  it 
is  sometimes  desirable  .to  make  low-power  sketches  of  the  speci- 
men. In  most  cases,  however,  only  sufficient  time  should  be 
spent  in  studying  the  specimen  to  give  an  idea  of  the  size,  struc- 

25 


26  HISTOLOGY   OF   MEDICINAL   PLANTS 

ture,  and  general  arrangement  or  plan  or  structure  if  a  section 
of  a  plant,  or,  if  a  powder,  to  note  its  striking  characters.  All 
the  finer  details  of  structure  are  best  brought  out  with  the 
high-power  objective  in  position. 

In  placing  the  high-power  objective  in  position,  it  is  first 
necessary  to  raise  the  body  by  the  coarse  adjustment;  then 
open  the  iris  diaphragm,  and  lower  the  body  until  the  objective 
is  within  about  one-eighth  of  an  inch  of  the  slide.  Now  raise 
the  tube  by  the  fine  adjustment  until  the  object  is  in  focus, 
then  gradually  close  the  iris  diaphragm  until  a  clear  definition 
of  the  object  is  obtained.  Now  proceed  to  make  an  accurate 
sketch  of  the  object  or  objects  being  studied. 

In  using  the  water  pr  oil-immersion  objectives  it  is  first 
necessary  to  place  a  drop  of  distilled  water  or  oil,  as  the  case 
may  be,  immediately  over  the  specimen,  then  lower  the  body 
by  the  coarse  adjustment  until  the  lens  of  the  objective  touches 
the  water  or  the  oil.  Raise  the  tube,  regulate  the  light  by  the 
iris  diaphragm,  and  proceed  as  if  the  high-power  objectives  were 
in  position. 

The  water  or  oil  should  be  removed  from  the  obiectives  and 
from  the  slide  when  not  in  use. 

After  the  higher-powered  objective  has  been  used,  the  body 
should  be  raised,  and  the  low-power  objective  placed  in  position. 
If  the  draw-tube  has  been  drawn  out  during  the  examination 
of  the  object,  replace  it,  but  be  sure  to  hold  one  hand  on  the 
nose-piece  so  as  to  prevent  scratching  the  objective  and  Abbe 
condenser  by  their  coming  in  forceful  contact.  Lastly,  clean 
the  mirror  with  a  soft  piece  of  linen.  In  returning  the  micro- 
scope to  its  case,  or  to  the  shelf,  grasp  the  limb,  or  the  pillar, 
firmly  and  carry  as  nearly  vertical  as  possible  in  order  not  to 
dislodge  the  eye-piece. 

ILLUMINATION 

The  illumination  for  microscopic  work  may  be  from  natural 
or  artificial  sources. 

It  has  been  generally  supposed  that  jthe  best  possible  illumi- 
nation for  microscopic  work  is  diffused  sunlight  obtained  from 
a  northern  direction.  No  matter  from  what  direction  diffused 


HOW.  TO   USE   THE   MICROSCOPE  27 

sunlight  is  obtained,  it  will  be  found  suitable  for  microscopic 
work.  In  no  case  should  direct  sunlight  be  used,  because  it 
will  be  found  blinding  in  its  effects  upon  the  eyes.  Natural 
illumination — diffused  sunlight — varies  so  greatly  during  the 
different  months  of  the  year,  and  even  during  different  periods 
of  the  day,  that  individual  workers  are  resorting  more  and  more 
to  artificial  illumination.  The  particular  advantage  of  such 
illumination  is  due  to  the  fact  that  its  quality  and  intensity 
are  uniform  at  all  times.  There  are  many  ways  of  securing 
such  artificial  illumination,  no  one  of  which  has  any  particular 
advantage  over  the  other.  Some  workers  use  an  ordinary  gas 
or  electric  light  with  a  color  screen  placed  in  the  sub-stage 
below  the  iris  diaphragm.  In  other  cases  a  globe  filled  with  a 
weak  solution  of  copper  sulphate  is  placed  in  such  a  way  be- 
tween the  source  of  light  and  the  microscope  that  the  light  is 


FIG.  30. — Micro  Lamp 

focused  on  the  mirror.  Modern  mechanical  ingenuity  has  de- 
vised, however,  a  number  of  more  convenient  micro  lamps 
(Fig.  30).  These  lamps  are  a  combination  of  light  and  screen. 
In  some  forms  a  number  of  different  screens  come  with  each 
lamp,  so  that  it  is  possible  to  obtain  white-,  blue-,  or  dark-ground 


28  HISTOLOGY  OF  MEDICINAL  PLANTS 

illumination.    The  type  of  the  screen  used  will  be  varied  accord- 
ing to  the  nature  of  the  object  studied. 

CARE  OF  THE  MICROSCOPE 

If  possible,  the  microscope  should  be  stored  in  a  room  of 
the  same  temperature  as  that  in  which  it  is  to  be  used.  In 
any  case,  avoid  storing  in  a  room  that  is  cooler  than  the  place 
of  use,  because  when  it  is  brought  into  a  warmer  room,  moisture 
will  condense  on  the  ocular  objectives  and  mirrors. 

Before  beginning  work  remove  all  moisture,  dust,  etc.,  from 
the  inner  and  outer  lenses  of  the  ocular,  the  objectives,  the 
Abbe  condenser,  and  the  mirror  by  means  of  a  piece  of  soft, 
old  linen.  When  the  work  is  finished  the  optical  parts  should 
be  thoroughly  cleaned. 

If  reagents  have  been  used,  be  sure  that  none  has  got  on 
the  objectives  or  the  Abbe  condenser.  If  any  reagent  has  got 
on  these  parts,  wash  it  off  with  water,  and  then  dry  them  thor- 
oughly with  soft  linen. 

The  inner  lenses  of  the  eye-pieces  and  the  under  lens  of  the 
Abbe  condenser  should  occasionally  be  cleaned.  The  mechani- 
cal parts  of  the  stand  should  be  cleaned  if  dust  accumulates,  and 
the  movable  surfaces  should  be  oiled  occasionally.  Never 
attempt  to  make  new  combinations  of  the  ocular  or  objective 
lenses,  or  transfer  the  objectives  or  ocular  from  one  microscope 
to  another,  because  the  lenses  of  any  given  microscope  form  a 
perfect  lens  system,  and  this  would  not  be  the  case  if  they  were 
transferred.  Keep  clean  cloths  in  a  dust-proof  box.  Under  no 
circumstances  touch  any  of  the  optical  parts  with  your  fingers. 

PREPARATION   OF  SPECIMENS  FOR  CUTTING 

Most  drug  plants  are  supplied  to  pharmacists  in  a  dried 
condition.  It  is  necessary,  therefore,  to  boil  the  drug  in  water, 
the  time  varying  from  a  few  minutes,  in  the  case  of  thin  leaves 
and  herbs,  up  to  a  half  hour  if  the  drug  is  a  thick  root  or  woody 
stem.  If  a  green  (undried)  drug  is  under  examination,  this 
first  step  is  not  necessary. 

If  the  specimen  to  be  cut  is  a  leaf,  a  flower-petal,  or  other 


HOW  TO  USE  THE  MICROSCOPE  29 

thin,  flexible  part  of  a  plant,  it  may  be  placed  between  pieces 
of  elder  pith  or  slices  of  carrot  or  potato  before  cutting. 


SHORT  PARAFFIN  PROCESS 

In  most  cases,  however,  more  perfect  sections  will  be  ob- 
tained if  the  specimens  are  embedded  in  paraffin,  by  the  quick 
paraffin  process,  which  is  easily  carried  out. 

After  boiling  the  specimen  in  water,  remove  the  excess  of 
moisture  from  the  outer  surface  with  filter  paper  or  wait  until 
the  water  has  evaporated.  Next  make  a  mould  of  stiff  card- 
board and  pour  melted  paraffin  (melting  at  50  or  60  degrees) 
into  the  mould  to  a  height  of  about  one-half  inch,  when  the 
paraffin  has  solidified.  This  may  be  hastened  by  floating  it 
on  cool  or  iced  water  instead  of  allowing  it  to  cool  at  room 
temperature. 

The  specimens  to  be  cut  are  now  placed  on  the  paraffin, 
with  glue,  if  necessary,  to  hold  them  in  position,  and  melted 
paraffin  poured  over  the  specimens  until  they  are  covered  to  a 
depth  of  about  one-fourth  of  an  inch.  Cool  on  iced  water, 
trim  off  the  outer  paraffin  to  the  desired  depth,  and  the  speci- 
men will  be  in  a  condition  suitable  for  cutting. 

Good  workable  sections  may  be  cut  from  specimens  embedded 
by  this  quick  paraffin  method.  After  a  little  practice  the  entire 
process  can  be  carried  out  in  less  than  an  hour.  This  method 
of  preparing  specimens  for  cutting  will  meet  every  need  of  the 
pharmacognosist. 

LONG  PARAFFIN  PROCESS 

In  order  to  bring  out  the  structure  of  the  protoplast  (living 
part  of  the  cell),  it  will  be  necessary  to  begin  with  the  living 
part  of  the  plant  and  to  use  the  long  paraffin  method  or  the 
collodion  method. 

Small  fragments  of  a  leaf,  stem,  or  root-tip  are  placed  in 
chromic-acid  solution,  acetic  alcohol,  picric  acid,  chromacetic 
acid,  alcohol,  etc.,  depending  upon  the  nature  of  the  specimen 
under  observation.  The  object  of  placing  the  living  specimen 
in  such  solutions  is  to  kill  the  protoplast  suddenly  so  that  the 
parts  of  the  cell  will  bear  the  same  relationship  to  each  other 


30  HISTOLOGY   OF   MEDICINAL   PLANTS 

that  they  did  in  the  living  plant,  and  to  fix  the  parts  so  killed. 
After  the  fixing  process  is  complete,  the  specimen  is  freed 
of  the  fixing  agent  by  washing  in  water.  From  the  water-bath 
the  specimens  are  transferred  successively  to  10,  20,  40,  60,  70, 
80,  90,  and  finally  100  per  cent  alcohol.  In  this  100  per  cent 
alcohol-bath  the  last  traces  of  moisture  are  removed.  The 


FIG.  31. — Paraffin-embedding  Oven 

length  of  time  required  to  leave  the  specimens  in  the  different 
percentages  of  alcohols  varies  from  a.  few  minutes  to  twenty- 
four  hours,  depending  upon  the  size  and  the  nature  of  the 
specimen. 

After  dehydration  the  specimen  is  placed  in  a  clearing  agent 
— chloroform  or  xylol — both  of  which  are  suitable  when  em- 
bedding in  paraffin.  The  clearing  agents  replace  the  alcohol  in 
the  cells,  and  at  the  same  time  render  the  tissues  transparent. 
From  the  clearing  agent  the  specimen  is  placed  in  a  weak  solu- 
tion of  paraffin,  dissolved  xylol,  or  chloroform.  The  strength  of 
the  paraffin  solution  is  gradually  increased  until  it  consists 
of  pure  paraffin.  The  temperature  of  the  paraffin-embedding 


HOW    TO   USE    THE    MICROSCOPE 


31 


oven  (Fig.  31)  should  not  be  much  higher  than  the  melting- 
point  of  the  paraffin. 

The  specimen  is  now  ready  to  be  embedded.  First  make  a 
mould  of  cardboard  or  a  lead-embedding  frame  (Fig.  32),  melt 
the  paraffin,  and  then  place  the 
specimen  in  a  manner  that  will 
facilitate  cutting.  Remove  the 
excess  of  paraffin  and  cut  when 
desired. 

In  using  the  collodion  method 
for     embedding     fibrous    speci- 
mens, as  wood,  bark,  roots,  etc., 
the  specimen  is  first  fixed  with  picric  acid,  wj 
cleared    in    ether-alcohol,  embedded 


FIG.  32.— Paraffin  Blocks 


and  twelve  per  cent  ether-alcohol 
embedded  in  a  pure  collodion 


CUTTING   SECTIONS 


Specimens  prepared  as  descril 
hand  microtome  or  a  machine  mi< 


ution,  anljMi 

DEPARTMENT 
OF 

ove  mayDejoit  wifSftr^*^'" 

"^8>°^R»        ^K 

C*Vs.«.- 

OF 


above 


HAND    MICROTOME 

In  cutting  sections  by  a  h&nd  microtome,  it  is  necessary  to 
place  the  specimen,  embedded  in  paraffin  or  held  between 
pieces  of  elder  pith,  carrot,  or  potato,  over  the  second  joints 
of  the  fingers,  then  press  the  first  joints  firmly  upon  the  speci- 
men with  the  thumb  pressed  against  it.  If  they  are  correctly 


FIG.  33. — Hand  Microtome 

held,  the  specimens  will  be  just  above  the  level  of  the  finger  and 
the  end  of  the  thumb,  and  the  joint  will  be  below  the  level  of 
the  finger. 

Hold  the  section  cutter  (Fig.  33)  firmly  in  the  hand  with 


32  HISTOLOGY  OF  MEDICINAL  PLANTS 

the  flat  surface  next  to  the  specimen.  While  cutting  the  sec- 
tion, press  your  arm  firmly  against  your  chest,  and  bend  the 
wrist  nearly  at  right  angles  to  the  arm.  Push  the  cutting  edge 
of  the  microtome  toward  the  body  and  through  the  specimen 
in  such  a  way  as  to  secure  as  thin  a  section  as  possible.  Do 
not  expect  to  obtain  nice,  thin  sections  during  the  first  or  second 
trials,  but*  continued  practice  will  enable  one  to  become  quite 
efficient  in  cutting  sections  in  this  manner. 

When  the  examination  of  drugs  is  a  daily  occurrence,  the 
above  method  will  be  found  highly  satisfactory. 

MACHINE  MICROTOMES 

When  a  number  of  sections  are  to  be  prepared  from  a  given 
specimen,  it  is  desirable  to  cut  the  sections  on  a  machine  micro- 
tome, particularly  when  the  sections  are  to  be  prepared  for  the 
use  of  students,  in  which  case  they  should  be  as  uniform  as 
possible. 

Great  care  should  be  exercised  in  cutting  sections  with  a 
machine  microtome — first,  in  the  selection  of  the  type  of  the 
microtome;  and  secondly,  in  the  style  of  knife  used  in  cutting. 

For  soft  tissues  embedded  in  paraffin  or  collodion,  the  rotary 
microtome  with  vertical  knife  will  give  best  results.  The  thick- 
ness of  the  specimen  is  regulated  by  mechanical  means,  so  that 
in  cutting  the  sections  it  i$  only  necessary  to  turn  a  crank  and 
remove  the  specimens  from  the  knife-edge,  unless  there  is  a 
ribbon-carrier  attachment.  If  the  sections  are  being  cut  from 
a  specimen  embedded  by  the  quick  paraffin  method,  it  is  best 
to  drop  the  section  in  a  metal  cup  partly  filled  with  warm  water. 
This  will  cause  the  paraffin  to  straighten  out,  and  the  specimen 
will  uncoil.  After  sufficient  specimens  have  been  cut,  the 
cup  should  be  placed  in  a  boiling-water  bath  until  the  paraffin 
surrounding  the  sections  melts  and  floats  on  the  water.  Before 
removing  the  specimen  from  the  water-bath,  it  is  advisable  to 
shake  the  glass  vigorously  in  order  to  cause  as  many  specimens 
as  possible  to  settle  to  the  bottom  of  the  cup.  The  cup  is  then 
placed  in  iced  water  or  set  aside  until  the  paraffin  has  solidified. 
The  cake-like  mass  is  then  removed  from  the  cup,  and  the  sec- 
tions adhering  to  its  under  surface  are  removed  by  lifting  them 
carefully  off  with  the  flat  side  of  the  knife  and  transferring  them, 


HOW   TO  USE  THE  MICROSCOPE  33 

together  with  the  sections  at  the  bottom  of  the  cup,  to  a  wide- 
mouth  bottle,  and  covered  with  alcohol,  glycerine,  and  water 
mixture;  or  if  it  is  desired  to  stain  the  specimens,  they  should 
be  placed  in  a  weak  alcoholic  solution. 

Specimens  having  a  hard,  woody  texture  should  be  cut  on 
a  sliding  microtome  by  means  of  a  special  wood  knife,  which 
is  especially  tempered  to  cut  woody  substances.  Woody  roots, 
wood,  or  thick  bark  may  be  cut  readily  on  this  microtome  when 
they  have  been  embedded  by  the  quick  paraffin  process.  The 
knife  in  the  sliding  microtome  is  placed  in  a  horizontal  position, 
slanting  so  that  the  knife-edge  is  drawn  gradually  across  the 
specimen.  After  cutting,  the  sections  are  treated  as  described 
above. 

The  thickness  of  the  sections  is  regulated  by  mechanical 
means.  After  a  section  has  been  cut,  the  block  containing  the 
specimen  is  raised  by  turning  a  thumb-screw.  In  this  microtome 
the  knife,  as  in  the  rotary  type,  is  fixed,  and  the  block  contain- 
ing the  specimen  is  movable. 

If  the  specimen  has  been  infiltrated  with,  and  embedded  in, 
paraffin  or  collodion,  the  treatment  of  the  sections  after  cutting 
should  be  different. 

In  the  case  of  paraffin,  the  sections  are  fastened  directly  to 
the  slide,  and  the  paraffin  is  dissolved  by  either  chloroform  or 
xylol.  The  specimen  is  then  placed  in  100,  95,  and  45  per  cent 
alcohol,  and  then  washed  in  water.  These  sections  are  now 
stained  with  water-stains,  brought  back  through  alcohol,  cleared, 
and  mounted  in  Canada  balsam. 

If  alcoholic  stains  are  used,  it  will  not  be  necessary  to  de- 
hydrate before  staining,  and  the  dehydration  after  staining  will 
also  be  eliminated.  ' 

Sections  infiltrated  with  collodion  are  either  stained  directly 
without  removing  the  collodion  or  after  removal. 

FORMS  OF  MICROTOMES 

The  hand  cylinder  microtome  (Fig.  34)  consists  of  a  cylindrical 
body.  The  clamp  for  holding  the  specimen  is  near  the  top 
below  the  cutting  surface.  At  the  lower  end  is  attached  a  microm- 
eter screw  with  a  divided  milled  head.  When  moved  forward 
one  division,  the  specimen  is  raised  o.oi  mm.  This  micrometer 


34  HISTOLOGY    OF   MEDICINAL   PLANTS 

screw  has  an  upward  movement  of  10  mm.     The  cutting  surface 
consists  of  a  cylindrical  glass  ring. 

The  hand  table  microtome  (Fig.  35)  is  provided  with  a  clamp, 
by  which  it  may  be  attached  to  the  edge  of  a  table  or  desk. 


FIG.  34. — Hand  Cylinder  Microtome 


FIG.  35. — Hand  Table  Microtome 


HOW   TO   USE    THE    MICROSCOPE  35 

The  cutting  surface  consists  of  two  separated  but  parallel  glass 
benches.  The  object  is  held  by  a  clamp  and  is  raised  by  a 
micrometer  screw,  which,  when  moved  through  one  division  by 
turning  the  divided  head,  raises  the  specimen  o.oi  mm. 

The  sliding  microtome  has  a  track  of  250  mm.  The  object 
is  held  by  a  clamp  and  its  height  regulated  by  hand.  The  disk 
regulating  the  micrometer  screw  is  divided  into  one  hundred 
parts.  When  this  is  turned  through  one  division,  the  object  is 
raised  0.005  mm-  or  5  microns,  at  the  same  time  a  clock-spring 
in  contact  with  teeth  registers  by  a  clicking  sound.  If  the  disk 
is  turned  through  two  divisions,  there  will  be  two  clicks,  etc. 
In  this  way  is'regulated  the  thickness  of  the  sections  cut.  When 
the  micrometer  screw  has  been  turned  through  the  one  hundred 
divisions,  it  must  be  unscrewed,  the  specimen  raised,  and  the 
steps  of  the  process  repeated.  The  knife  is  movable  and  is 
drawn  across  the  specimen  in  making  sections. 

T^he  base  sledge  microtome  (Fig.  36)  has  a  heavy  iron  base 
which  supports  a  sliding- way  on  which  the  object-carrier  moves. 


FIG.  36. — Base  Sledge  Microtome 

The  object-carrier  is  mounted  on  a  solid  mass  of  metal,  and  is 
provided  with  a  clamp  for  holding  the  object.  The  object  is 
raised  by  turning  a  knob  which,  when  turned  once,  raises  the 
specimen  one  to  twenty  microns,  according  to  how  the  feeding 
mechanism  is  set. 


36  HISTOLOGY  OF  MEDICINAL  PLANTS 

Sections  thicker  than  twenty  microns  may  be  obtained  by 
turning  the  knob  two  or  more  times.  The  knife  is  fixed  and  is 
supported  by  two  pillars,  the  base  of  which  may  be  moved  for- 
ward or  backward  in  such  a  manner  that  the  knife  can  be 
arranged  with  an  oblique  or  right-angled  cutting  surface. 

The  Minot  rotary  microtome  (Fig.  37)  has  a  fixed  knife,  held 
in  position  by  two  pillars,  and  a  movable  object-carrier.  The 


FIG.  37. — Minot  Rotary  Microtome 

object  is  firmly  secured  by  a  clamp,  and  it  is  raised  by  a  microm- 
eter screw.  The  screw  is  attached  to  a  wheel  having  five 
hundred  teeth  on  its  periphery.  A  pawl  is  adjusted  to  the  teeth 
in  such  a  way  that,  when  moved  by  turning  a  wheel  to  which 
it  is  attached,  specimens  varying  from  one  to  twenty-five  microns 
in  thickness  may  be  cut,  according  to  the  way  the  adjusting  disk 
is  set.  When  the  mechanism  has  been  regulated  and  the  object 
adjusted  for  cutting,  it  is  only  necessary  to  turn  a  crank  in 
cutting  sections. 

CARE  OF  MICROTOMES 

When  not  in  use,  microtomes  should  be  protected  from  dust, 
and  all  parts  liable  to  friction  should  be  oiled. 


HOW   TO  USE  THE  MICROSCOPE  37 

Microtome  knives  should  be  honed  as  often  as  is  necessary 
to  insure  a  proper  cutting  edge.  After  cutting  objects,  the 
knives  should  be  removed,  cleaned,  and  oiled. 

It  should  be  kept  clearly  in  mind  that  special  knives  are 
required  for  cutting  collodion,  paraffin,  and  frozen  and  woody 
sections.  The  cutting  edges  of  the  different  knives  vary  con- 
siderably, as  is  shown  in  the  preceding  cuts. 


CHAPTER  V 

REAGENTS 

Little  attention  is  given  in  the  present  work  to  micro-chemical 
reactions  for  the  reason  that  their  value  has  been  much  over- 
rated in  the  past.  A  few  reagents  will  be  found  useful,  however, 
and  these  few  are  given,  as  well  as  their  special  use.  They  are 
as  follows: 

LIST   OF  REAGENTS 

Distilled  Water  is  used  in  the  alcohol,  glycerine,  and  water 
mixture  as  a  general  mounting  medium.  It  is  used  when  warm 
as  a  test  for  inulin  and  it  is  used  in  preparing  various  reagents. 

Glycerine  is  used  in  preparing  the  alcohol,  glycerine,  and 
water  mixture,  in  testing  for  aleurone  grains,  and  as  a  temporary 
mounting  medium. 

.  Alcohol  is  used  in  preparing  the  alcohol,  glycerine,  and  water 
mixture,  in  testing  for  volatile  oils. 

Acetic  Acid.  Both  dilute  and  strong  solutions  are  used  in 
testing  for  aleurone  grains,  cystoliths,  and  crystals  of  calcium 
oxalate. 

Hydrochloric  Acid  is  used  in  connection  with  phloroglucin 
as  a  test  for  lignin  and  as  a  test  for  calcium  oxalate. 

Ferric  Chloride  Solution  is  used  as  a  test  for  tannin. 

Sulphuric  Acid  is  used  as  a  test  for  calcium  oxalate. 

Tincture  Alkana  is  used  when  freshly  prepared  by  macerat- 
ing the  granulated  root  with  alcohol  and  filtering,  as  a  test 
for  resin. 

Sodium  Hydroxide.  A  five  per  cent  solution  is  used  as  a 
test  for  suberin  and  as  a  clearing  agent. 

Copper  Ammonia  is  used  as  a  test  for  cellulose. 

Ammonical  Solution  of  Potash  is  used  as  a  test  for  fixed 
oils.  The  solution  is  a  mixture  of  equal  parts  of  a  saturated 
solution  of  potassium  hydroxide  and  stronger  ammonia. 

38 


REAGENTS  39 

Oil  of  Cloves  is  used  as  a  clearing  fluid  for  sections  pre- 
paratory to  mounting  in  Canada  balsam. 

Canada  Balsam  is  used  as  a  permanent  mounting  medium 
for  dehydrated  specimens,  and  as  a  cement  for  ringing  slides. 

Paraffin  is  used  for  general  embedding  and  infiltrating. 

Lugol's  Solution  is  used  as  a  test  for  starch  and  for  aleurone 
grains  and  proteid  matters. 

Osmic  Acid.  A  two  per  cent  solution  is  used  as  a  test  for 
fixed  oils. 

Alcohol,  Glycerine,  and  Water  Mixture  is  used  as  a  tem- 
porary mounting  medium  and  as  a  qualitative  test  for  fixed  oils. 

Chlorzinc  Iodide  is  used  as  a  test  for  suberin,  lignin,  cellulose, 
and  starch. 

Analine  Chloride  is  used  as  a  test  for  lignified  cell  walls  of 
bast  fibres  and  of  stone  cells. 

Phloroglucin.  A  one  per  cent  alcoholic  solution  is  used  in 
connection  with  hydrochloric  acid  as  a  test  for  lignin. 

Haematoxylin-Delifields  is  used  as  a  test  for  cellulose. 

REAGENT   SET 

Each  worker  should  be  provided  with  a  set  of  reagent  bottles 
(Fig.  38).  Such  a  set  may  be  selected  according  to  the  taste 


FIG.  38. — Reagent  Set 

of  the  individual,  but  experience  has  shown  that  a  30  c.c.  bottle 
with  a  ground-in  pipette  and  a  rubber  bulb  is  preferable  to  other 
types.  In  such  forms  the  pipettes  are  readily  cleaned,  and  the 
rubber  bulbs  can  be  replaced  when  they  become  old  and  brittle. 


40 


HISTOLOGY   OF   MEDICINAL  PLANTS 


The  entire  set  should  be  protected  from  dust  by  keeping  it  in  a 
case,  the  cover  of  which  should  be  closed  when  the  set  is  not 
in  use. 

MEASURING   CYLINDER 

In  order  accurately  to  measure  micro-chemical  reagents,  it 
is  necessary  to  have  a  standard  50  c.c.  cylinder  (Fig.  39)  graduated 


FlG.  39. — Measuring  Cylinder  FIG.  40. — Staining  Dish 

to  c.c.'s.     Such  a  cylinder  should  form  a  part  of  the  reagent  set. 

STAINING  DISHES 

There  is  a  great  variety  of  staining  dishes  (Fig.  40),  but 
for  general  histological  work  a  glass  staining  dish  with  groves 
for  holding  six  or  more  slides  and  a  glass  cover  is  most  desirable. 


CHAPTER  VI 

HOW  TO  MOUNT  SPECIMENS 

The  method  of  procedure  in  mounting  specimens  for  study 
varies  according  to  the  nature  of  the  specimen,  its  preliminary 
treatment,  and  the  character  of  the  mount  to  be  made.  As  to 
duration,  mounts  are  either  temporary  or  permanent. 

TEMPORARY  MOUNTS 

In  preparing  a  temporary  mount,  place  the  specimen  in  the 
centre  of  a,  clean  slide  and  add  two  or  more  drops  of  the  tem- 
porary mounting  medium,  which  may  be  water,  or  a  mixture 
of  equal  parts  of  alcohol,  glycerine,  and  water,  or  some  micro- 
chemical  reagent,  as  weak  Lugol's  solution,  solution  of  chloral 
hydrate,  etc.  Cover  this  with  a  cover  glass  and  press  down 
gently.  Remove  the  excess  of  the  mounting  medium  with  a 
piece  of  blotting  paper.  Now  place  the  slide  on  the  stage  and 
proceed  to  examine  it.  Such  mounts  can  of  course  be  used  only 
for  short  periods  of  study;  and  when  the  period  of  observation 
is  finished,  the  specimen  should  be  removed  and  the  slide  washed, 
or  the  slide  washing  may  be  deferred  until  a  number  of  such 
slides  have  accumulated.  At  any  rate,  when  the  mounting 
medium  dries,  the  specimen  is  no  longer  suitable  for  observation. 

PERMANENT  MOUNTS 

Permanent  mounts  are  prepared  in  much  the  same  way  as 
temporary,  but  of  course  the  mounting  medium  is  different. 
The  kind  of  permanent  mounting  medium  used  depends  upon 
the  previous  treatment  of  the  specimen.  If  the  specimen  has 
been  preserved  in  alcohol  or  glycerine  and  water,  it  is  usually 
mounted  in  glycerine  jelly.  If  the  specimen  in  question  is  a 
powder,  it  is  placed  in  the  centre  of  the  slide  and  a  drop  or  two 

41 


42  HISTOLOGY   OF   MEDICINAL   PLANTS 

of  glycerine,  alcohol,  and  water  mixture  added,  unless  the 
powder  was  already  in  suspension  in  such  a  mixture.  Cut  a 
small  cube  of  glycerine  jelly  and  place  it  in  the  centre  of  the 
powder  mixture.  Lift  up  the  slide  by  means  of  pliers,  or  grasp 
the  two  edges  between  the  thumb  and  finger  and  hold  over  a 
small  flame  of  an  alcohol  lamp,  or  place  on  a  steam-bath  until 
the  glycerine  jelly  has  melted.  Next  sterilize  a  dissecting  needle, 
cool,  and  mix  the  powder  with  the  glycerine  jelly,  being  careful 
not  to  lift  the  point  of  the  needle  from  the  slide  during  the 
operation.  If  the  mixing  has  been  carefully  done,  few  or  no 
air-bubbles  will  be  present;  but  if  they  are  present,  heat  the 
needle,  and  while  it  is  white  hot  touch  the  bubbles  with  its 
point,  and  they  will  disappear.  Now  take  a  pair  of  forceps  and, 
after  securing  a  clean  cover  glass  near  the  edge,  pass  them  three 
times  through  the  flame  of  the  alcohol  lamp.  While  holding  it 
in  a  slanting  position,  touch  one  side  of  the  powder  mixture  and 
slowly  lower  the  cover  glass  until  it  comes  in  complete  contact 
with  the  mixture.  Now  press  gently  with  the  end  of  the  needle- 
handle,  and  set  it  aside  to  cool.  When  it  is  cool,  place  a  neatly 
trimmed  label  on  one  end  of  the  slide,  on  which  write  the  name 
of  the  specimen,  the  number  of  the  series  of  which  it  is  to  form 
a  part,  etc.  Any  excess  of  glycerine  jelly,  which  may  have 
been  pressed  out  from  the  edges  of  the  cover  glass,  should  not 
be  removed  at  once,  but  should  be  allowed  to  remain  on  the 
slide  for  at  least  one  month  in  order  to  allow  for  shrinkage  due 
to  evaporation.  At  the  end  of  a  month  remove  the  glycerine 
jelly  by  first  passing  the  blade  of  a  knife,  held  in  a  vertical 
position,  the  back  of  the  knife  being  next  to  the  slide,  around 
the  edge  of  the  cover  glass.  After  turning  the  knife-blade  so 
that  the  flat  side  is  in  contact  with  slide,  remove  the  jelly  outside 
of  the  cover  glass.  Any  remaining  fragments  should  be  removed 
with  a  piece  of  old  linen  or  cotton  cloth.  Finally,  ring  the  edge 
of  the  cover  glass  with  microscopical  cement,  of  which  there 
are  many  types  to  be  had.  If  the  cleaning  has  been  done 
thoroughly,  there  is  no  better  ringing  cement  than  Canada 
balsam. 

In  mounting  cross-sections,  the  method  of  procedure  is 
similar  to  the  above,  with  the  exception  that  the  glycerine  jelly 
is  placed  at  the  side  of  the  specimen  and  not  in  the  centre. 


HOW   TO   MOUNT   SPECIMENS  43 

While  melting  the  jelly,  incline  the  slide  in  order -to  allow  the 
melted  glycerine  jelly  to  flow  gradually  over  the  specimen,  thus 
replacing  the  air  contained  in  the  cells  and  intercellular  spaces. 
Finish  the  mounting  as  directed  above,  but  under  no  conditions 
should  you  stir  the  glycerine  jelly  with  the  section. 

If  specimens,  after  having  been  embedded  in  paraffin  or 
collodion,  are  cut,  cleared,  stained,  and  dehydrated,  they  are 
usually  mounted  in  Canada  balsam.  A  small  drop  of  this  sub- 
stance, which  may  be  obtained  in  collapsible  tubes,  is  placed 
at  one  side  of  the  specimen.  While  inclining  the  slide,  gently 
heat  until  the  Canada  balsam  covers  the  specimen.  Secure  a 
cover  glass  by  the  aid  of  pliers,  pass  it  through  the  flame  three 
times,  and  lower  it  slowly  while  holding  it  in  an  inclined  position. 
Press  gently  on  the  cover  glass  with  the  needle-handle,  and  keep 
in  a  horizontal  position  for  twenty-four  hours,  then  place  directly 
in  a  slide  box  or  cabinet,  since  no  sealing  is  required. 

Glycerine  is  sometimes  used  to  make  permanent  mounts,  but 
it  is  unsatisfactory,  because  the  cover  glass  is  easily  removed 
and  the  specimen  spoiled  or  lost,  unless  ringed — a  procedure 
which  is  not  easily  accomplished.  If  the  specimen  is  to  be 
mounted  in  glycerine,  it  must  first  be  placed  in  a  mixture  of 
alcohol,  glycerine,  and  water,  and  then  transferred  to  glycerine. 
Lactic  acid  .is  another  permanent  liquid-mounting  medium, 
which  is  unsatisfactory  in  the  same  way  as  glycerine,  but  like 
glycerine,  there  are  certain  special  cases  where  it  is  desirable 
to  use  it.  When  this  is  used,  the  slides  should  be  kept  in  a 
horizontal  position,  unless  ringed. 

COVER   GLASSES 

Great  care  should  be  used  In  the  selection  of  cover  glasses, 
however,  not  only  as  regards  their  shape  but  as  to  their  thickness. 
The  standard  tube  length  of  the  different  manufacturers  makes 
an  allowance  of  a  definite  thickness  for  cover  glasses.  It  is 
necessary,  therefore,  to  use  cover  glasses  made  by  the  manu- 
facturer of  the  microscope  in  use. 

Cover  glasses  are  either  square  or  round.  Of  each  there  are 
four  different  thicknesses  and  two  different  sizes.  The  standard 
thicknesses  are: 


44 


HISTOLOGY   OF   MEDICINAL  PLANTS 


The   small  .size   is    designated    three-fourths    and    the    large 
size  seven-eighths. 

Cover  glasses  are  circular  (Fig.  41),  square  (Fig.  42),  or 
rectangular  (Fig.  43)  pieces  of  transparent  glass  used  in  covering 
the  specimens  mounted  on  glass  slides.  A  few  years  ago  much 
difficulty  was  experienced  in  obtaining  uniformly  thick  and 


£.  LtlTZ  WC 


FIG.  41. — Round 
Cover  Glass 


FlG.  42. — Square 
Cover  Glass 


FIG.  43. — Rectangular  Cover 
Glass 


transparent  cover  glasses,  but  no  such  difficulty  is  experienced 
to-day.  The  type  of  cover  glass  used  depends  largely  upon  the 
character  of  the  specimen  to  be  mounted.  The  square  and 
rectangular  glasses  are  selected  when  a  series  of  specimens  are 
to  be  mounted,  but  in  mounting  powdered  drugs  and  histological 
specimens  the  round  cover  glasses  are  preferable  because  they 
are  more  sightly  and  more  readily  cleaned  and  rinsed. 

GLASS   SLIDES 

Glass  slides  (Fig.  44)  are  rectangular  pieces  of  transparent 
glass  used  as  a  mounting  surface  for  microscopic  objects.    The 


FIG.  44.— Glass  Slide 

slides  are  usually  three  inches  long  by  one  inch  wide,  and  they 
should  be  composed  of  white  glass,  and  they  should  have  ground 


HOW  TO  MOUNT   SPECIMENS 


45 


and  beveled  edges.     Slides  should  be  of  uniform  thickness,  and 
they  should  not  become  cloudy  upon  standing 

SLIDE  AND  COVER-GLASS  FORCEPS 

Slides  and  cover  glasses  should  be  grasped  by  their  edges. 
To  the  beginner  this  is  not  easy.  In  order  to  facilitate  holding 
slides  and  cover  glasses  during  the  mounting  process,  one  may 
use  a  slide  and  a  cover-glass  forceps.  The  slide  forceps  consists 
of  wire  bent  and  twisted  in  such  a  way  that  it  holds  a  slide 
firmly  when  attached  to  its  two  edges. 

There  are  various  forms  of  cover-glass  holders,  but  only  two 
types  as  far  as  the  method  of  securing  the  cover  glass  is  con- 


FIG.  45. — Histological  Forceps 

cerned.  First,  there  are  the  bacteriological  and  the  histological 
forceps  (Fig.  45),  which  are  self-closing.  The  two  blades  of  such 
forceps  must  be  forced  apart  by  pressure  in  securing  the  cover 
glass.  The  second  type  of  forceps  is  that  in  which  the  two 
blades  are  normally  separated  (Fig.  46),  it  being  necessary  to 


FIG.  46. — Forceps 

press  the  blades  to  either  side  of  the  cover  glass  in  order  to 
secure  and  hold  it.     There  is  a  modification  of  this  type  of 


FlG.  47. — Sliding-pin  Forceps 

forceps  which  enables  one  to  lock  the  blades  by  means  of  a  slid- 
ing pin  (Fig.  47),  after  the  cover  glass  has  been  secured.     It  is 


46  HISTOLOGY   OF   MEDICINAL  PLANTS 

v 

well  to  accustom  oneself  to  one  type,  for  by  so  doing  one  may 
become  dexterous  in  its  use. 

NEEDLES 

Two  dissecting  needles  (Fig.  48)  should  form  a  part  of  the 
histologist's  mounting  set.     The  handles  mav  be  of  any  material, 


FIG.  48. — Dissecting  Needle 

but  the  needle  should  be  of  tempered  steel  and  about  two  inches 
long. 

SCISSORS 

Almost  any  sort  of  scissors  (Fig.  49)  will  do  for  histology 
work,  but  a  small  scissors  with  fine  pointed  blades,  are  preferred. 


FIG.  49. — Scissors 

Scissors  are  useful  in  trimming  labels  and  in  cutting  strips  of 
leaves  and  sections  of  fibrous  roots  that  are  to  be  embedded 
and  cut. 

SCALPELS 

Scalpels  (Fig.  50)  have  steel  blades  and  ebony  handles. 
These  vary  in  regard  to  size  and  quality  of  material.  The 
cheaper  grades  are  quite  as  satisfactory,  however,  as  the  more 
expensive  ones,  and  for  general  use  a  medium-sized  blade  and 
handle  will  be  found  most  useful. 

TURNTABLE 

Much  time  and  energy  may  be  saved  by  ringing  slides  on  a 
turntable  (Fig.  51).  There  is  a  flat  surface  upon  which  to  rest 
the  hand  holding  the  brush  with  cement,  and  a  revolving  table 


HOW   TO   MOUNT   SPECIMENS 


47 


upon  which  the  slide  to  be  ringed  is  held  by  means  of  two  clips. 
In  ringing  slides,  it  is  only  necessary  to  revolve  the  table,  and 


FIG.  50. — Scalpels 


FIG.  51. — Turntable 

at  the  same  time  to  transfer  the  cement  to  the  edge  of  the 
cover  glass  from  the  brush  held  in  the  hand. 


LABELING 


There  are  many  ways  of  labeling  slides,  but  the  best  method 
is  to  place  on  the  label  the  name  of  the  specimen,  the  powder 


48 


HISTOLOGY   OF   MEDICINAL   PLANTS 


number,    and    the    box,    the    tray    or   cabinet  number.     For 
example: 

Powdered  Arnica  Flowers 
No.  80 — Box  A — 600. 

PRESERVATION   OF   MOUNTED    SPECIMENS 

Accurately  mounted,  labeled,  and  ringed  slides  should  be 
filed  away  for  future  study  and  reference.     Such  filing  may 


FIG.  52. — Slide  Box 


FIG.  53.— Slide  Tray 

be  done  in  slide  boxes,  in  slide  trays,  or  in  cabinets.     Slide 
boxes  are  to  be  had  of  a  holding  capacity  varying  from  one  to 


HOW   TO   MOUNT   SPECIMENS  49 

one  hundred  slides.  For  general  use,  slide  boxes  (Fig.  52)  hold- 
ing one  hundred  slides  will  be  found  most  useful.  Some  workers 
prefer  trays  (Fig.  53),  because  of  the  saving  of  time  in  selecting 
specimens.  Trays  hold  twenty  slides  arranged  in  two  rows. 
The  cover  of  the  tray  is  divided  into  two  sections  so  that,  if 


FIG.  54. — Slide  Cabinet 

desired,  only  one  row  of  slides  is  uncovered  at  a  time.  Slide 
cabinets  (Fig.  54)  are  particularly  desirable  for  storing  large 
individual  collections,  particularly  when  the  slides  are  used 
frequently  for  reference.  Large  selections  of  slides  should  be 
numbered  and  card  indexed  in  order  to  facilitate  finding. 


Part  II 
TISSUES    CELLS,  AND  CELL  CONTENTS 


CHAPTER  I 

THE    CELL 

The  cell  is  the  unit  of  structure  of  all  plants.  In  fact  the 
cell  is  the  plant  in  many  of  the  lower  forms — so  called  unicellular 
plants.  All  plants,  then,  consist  of  one  or  more  cells. 

While  cells  vary  greatly  in  size,  form,  color,  contents,  and 
function,  still  in  certain  respects  their  structure  is  identical. 

TYPICAL  CELL 

The  typical  vegetable  cell  is  composed  of  a  living  portion  or 
protoplast  and  an  external  covering,  or  wall.  The  protoplast  in- 
cludes everything  within  the  wall.  It  is  made  up  of  a  number 
of  parts,  each  part  performing  certain  functions  yet  harmonizing 
with  the  work  of  the  cell  as  a  whole.  The  protoplast  (proto- 
plasm) is  a  viscid  substance  resembling  the  white  of  an  egg. 
The  protoplast,  when  unstained  and  unmagnified,  appears 
structureless,  but  when  stained  with  dyes  and  magnified,  it  is 
found  to  be  highly  organized.  The  two  most  striking  parts  of 
the  protoplast  are  the  cytoplasm  and  the  nucleus.  The  part 
of  the  protoplast  lining  the  innermost  part  of  the  wall  is  the 
ectoplast,  which  is  less  granular  and  slightly  denser  than  most 
of  the  cytoplasm.  The  cytoplasm  is  decidedly  granular  in 
structure. 

In  the  cytoplasm  occurs  one  or  more  cavities,  vacuoles,  filled 
with  cell  sap.  Embedded  in  the  cytoplasm  are  numerous 
chromatophores,  which  vary  in  color  in  the  different  cells,  from 
colorless  to  yellow,  to  red,  and  to  green.  The  nucleus  is  the 
seat  of  the  vital  activity  of  the  cell,  and  the  seat  of  heredity. 
The  whole  life  and  activity  of  the  cell  centre,  therefore,  in  and 
about  the  nucleus. 

The  outer  portion  of  the  nucelus  consists  of  a  thin  membrane 
or  wall.  The  membrane  encloses  numerous  granular  particles— 

53 


54  HISTOLOGY   OF  MEDICINAL  PLANTS 

• 

chromatin — which  are  highly  susceptible  to  organic  stains. 
Among  the  granules  are  thread-like  particles  or  linin.  Near 
the  centre  of  the  nucelus  are  one  or  more  small  rounded  nucleoli. 
The  liquid  portion  of  the  nucleus,  filling  the  membranes  and 
surrounding  the  chromatin,  linin,  and  nucleoli,  is  the  nuclear 
sap. 

Other  cell  contents  characteristic  of  certain  cells  are  crystals, 
starch,  aleurone,  oil,  and  alkaloids.  The  detailed  discussion  of 
these  substances  will  be  deferred  until  a  later  chapter. 

The  cell  wall  which  surrounds  the  protoplast  is  a  product  of 
its  activity.  The  structure  and  composition  of  the  wall  of  any 
given  cell  vary  according  to  the  ultimate  function  of  the  cell. 
The  walls  may  be  thin  or  thick,  porous  or  non-porous,  and 
colored  or  colorless.  The  composition  of  cell  walls  varies  greatly. 
The  majority  of  cell  walls  are  composed  of  cellulose,  in  other 
cells  of  linin,  in  others  of  cutin,  and  in  still  others  of  suberin,  etc. 
In  the  majority  of  cells  the  walls  are  laid  down  in  a  series  of 
layers  one  over  the  other  by  apposition,  similar  to  the  manner 
of  building  a  pile  of  paper  from  separate  sheets.  The  first  layer 
is  deposited  over  the  primary  wall,  formed  during  cell  division; 
to  this  is  added  another  layer,  etc.  A  modification  of  this 
manner  of  growth  is  that  in  which  the  layers  are  built  up  one 
over  the  other,  but  the  building  is  gradually  done  by  the  deposit 
of  minute  particles  of  cell-wall  substance  over  the  older  de- 
posits. Such  walls  are  never  striated,  as  is  likely  to  be  the  case 
in  cell  walls  formed  by  the  first  method.  In  other  cells  the  walls 
are  increased  in  thickness  by  the  deposition  of  new  wall  material 
in  the  older  membrane.  The  cell  walls  will  be  discussed  more 
fully  when  the  different  tissues  are  studied  in  detail. 

INDIRECT   CELL  DIVISION    (KARYOKINESIS) 

The  purpose  of  cell  division  is  to  increase  the  number  of  cells 
of  a  tissue,  an  organ,  an  organism,  or  to  increase  the  number  of 
organisms,  etc.  Such  cell  divisions  involve,  first,  an  equal 
division  of  the  protoplast  and,  secondly,  the  formation  of  a  wall 
between  the  divided  protoplasts.  The  first  changes  in  structure 
of  a  cell  undergoing  division  occur  in  the  nucleus. 


THE   CELL  55 

CHANGES   IN  A   CELL   UNDERGOING   DIVISION 

The  linin  threads  become  thicker  and  shorter.  The  chro- 
matin  granules  increase  in  size  and  amount;  the  threads  and 
chromatin  granules  separate  into  a  definite  number  of  segments 
or  chromosomes  (Plate  i,  Fig.  2).  The  nuclear  membrane  be- 
comes invested  with  .a  fibrous  protoplasmic  layer  which  later 
separates  and  passes  into  either  end  of  the  cell,  there  forming 
the  polar  caps  (Plate  i,  Fig.  3). 

The  nuclear  membrane  and  the  nucleoli  disappear  at  about 
this  time.  Two  fibres,  one  from  each  polar  cap,  become  at- 
tached to  opposite  sides  of  the  individual  chromosomes.  Other 
fibres  from  the  two  polar  caps  unite  to  form  the  spindle  fibres, 
which  thus  extend  from  pole  to  pole.  All  these  spindle  fibres 
form  the  nuclear  spindle  (Plate  i,  Fig.  5). 

The  chromosomes  now  pass  toward  the  division  centre  of 
the  cell  or  equatorial  plane  and  form,  collectively,  the  equatorial 
plate  (Plate  i,  Fig.  5).  At  this  point  of  cell  division,  the  chromo- 
somes are  U-shaped,  and  the  curved  part  of  the  chromosomes 
faces  the  equatorial  plane.  The  chromosomes  finally  split  into 
two  equal  parts  (Plate  i,  Fig.  6).  The  actual  separation  of  the 
halves  of  chromosomes  is  brought  about  by  the  attached  polar 
fibres,  which  contract  toward  the  polar  caps  (Plate  i,  Fig.  7). 
The  chromosomes  are  finally  drawn  to  the  polar  caps  (Plate  i, 
Fig.  8).  The  chromosomes  now  form  a  rounded  mass.  They 
then  separate  into  linin  threads  and  chromatin  granules.  Nuc- 
leoli reappear,  and  nuclear  sap  forms.  Finally,  a  nuclear  mem- 
brane develops.  The  spindle  fibres,  which  still  extend  from 
pole  to  pole,  become  thickened  at  the  equatorial  plane  (Plate  i, 
Fig.  8) ,  and  finally  their  edges  become  united  to  form  the  cell- 
plate  (Plate  i,  Fig.  9),  which  extends  across  the  cell,  thus  com- 
pletely separating  the  mother  cell  into  two  daughter  cells.  After 
the  formation  of  the  cell-plate,  the  spindle  fibres  disappear. 
The  cell  becomes  modified  to  form  the  middle  lamella,  on  either 
side  of  which  the  daughter  protoplast  adds  a  cellulose  layer. 
The  ultimate  composition  of  the  middle  lamella  and  the  com- 
position and  structure  of  the  cell  wall  will  differ  according  to 
the  function  which  the  cell  will  finally  perform. 


PLATE   i 


THE    CELL  57 


ORIGIN  OF  MULTICELLULAR  PLANTS 

All  multicellular  plants  are  built  up  by  the  repeated  cell 
division  of  one  original  cell.  If  the  cells  formed  are  similar  in 
structure  and  function,  they  form  a  tissue.  In  multicellular 
plants  many  different  kinds  of  tissues  will  be  formed  as  a  result 
of  cell  division,  since  there  are  many  different  functions  to  be 
performed  by  such  an  organism.  When  several  of  these  tissues 
become  associated  and  their  functions  are  correlated,  they  form 
an  organ.  The  association  of  several  organs  in  one  form  makes 
an  organism.  The  oak-tree  is  an  organism.  It  is  made  up  of 
organs  known  as  flowers,  leaves,  stems,  roots,  etc.  Each  of 
these  organs  is  in  turn  made  up  of  several  kinds  of  tissue.  In 
some  cases  it  is  difficult  to  designate  a  single  function  to  an 
aggregation  of  cells  (tissue).  In  fact,  a  tissue  may  perform 
different  functions  at  different  periods  of  its  existence  or  it 
may  perform  two  functions  at  one  and  the  same  time;  as  an 
example,  stone  cells,  whose  primary  function  is  mechanical,  in 
many  cases  function  as  storage  tissue.  The  cells  forming  the 
tissues  of  the  plant,  in  fact,  show  great  adaptability  in  regard 
to  the  function  which  they  perform.  Nevertheless  there  is  a 
predominating  function  which  all  tissues  perform,  and  the 
structure  of  the  cells  forming  such  tissues  is  so  uniform  that  it 
is  possible  to  classify  them. 

The  functional  classification  of  tissues  is  chosen  for  the 
purpose  of  demonstrating  the  adaptation  of  cell  structure  to 
cell  function.  If  the  cells  performing  a  similar  function  in  the 
different  plants  were  identical  in  number,  distribution,  form, 
color,  size,  structure,  and  cell  contents,  there  would  not  be  a 
science  of  histology  upon  which  the  art  of  microscopic  pharma- 
cognosy  is  based.  It  may  be  said,  however,  with  certainty, 
that  the  cells  forming  certain  of  the  tissues  of  any  given  species 
of  plant  will  differ  in  a  recognizable  degree  from  cells  perform- 
ing a  similar  function  in  other  species  of  plants.  Often  a  tissue 
is  present  in  one  plant  but  absent  in  another.  For  example, 
many  aquatic  plants  are  devoid  of  mechanical  fibrous  cells. 
The  barks  of  certain  plants  have  characteristic  stone  cells,  while 
in  many  other  barks  no  stone  cells  occur.  Many  leaves  have 
characteristic  trichomes;  others  are  free  from  trichomes,  etc. 


58  HISTOLOGY   OF   MEDICINAL   PLANTS 

Yet  all  cells  performing  a  given  function  will  structurally  re- 
semble each  other.  In  the  present  work  the  nucleus  and  other 
parts  of  the  living  protoplast  will  not  be  considered,  for  the 
reason  that  these  parts  are  not  in  a  condition  suitable  for  study, 
because  most  drugs  come  to  market  in  a  dried  condition,  a  con- 
dition which  eliminates  the  possibility  of  studying  the  proto- 
plast. The  general  structure  of  the  cells  forming  the  different 
tissues  will  first  be  considered,  then  their  variation,  as  seen  in 
different  plants,  and  finally  their  functions. 


CHAPTER  II 

THE  EPIDERMIS  AND   PERIDERM 

The  epidermis  and  its  modifications,  the  hypodermis  and 
the  periderm,  form  the  dermal  or  protective  outer  layer  or  layers 
of  the  plant. 

The  epidermis  of  most  leaves,  stems  of  herbs,  seeds,  fruits, 
floral  organs,  and  young  woody  stems  consists  of  a  single  layer 
of  cells  which  form  an  impervious  outer  covering,  with  the 
exception  of  the  stoma. 

LEAF  EPIDERMIS 

The  cells  of  the  epidermis  vary  in  size,  in  thickness  of  the 
side  and  end  walls,  in  form,  in  arrangement,  in  character  of 
outgrowths,  in  the  nature  of  the  surface  deposits,  in  the  char- 
acter of  wall — whether  smooth  or  rough — and  in  size. 

In  cross-sections  of  the  leaf  the  character  of  both  the  side 
and  end  walls  is  easily  studied. 

In  surface  sections — the  view  most  frequently  seen  in  pow- 
ders— the  side  walls  are  more  conspicuous  than  the  end  wall 
(Plates  2  and  3).  This  is  so  because  the  light  is  considerably  re- 
tarded in  passing  through  the  entire  length  of  the  side  walls, 
while  the  light  is  retarded  only  slightly  in  passing  through  the 
end  wall.  The  light  in  this  case  passes  through  the  width 
(thickness)  of  the  wall  only.  The  outer  walls  of  epidermal  cells 
are  characteristic  only  when  they  are  striated,  rough,  pitted, 
colored,  etc.  In  the  majority  of  leaves  the  outer  wall  of  the 
epidermal  cells  is  not  diagnostic  in  powders,  or  in  surface 
sections. 

The  thickness  of  the  end  and  side  walls  of  epidermal  cells 
differs  greatly  in  different  plants. 

As  a  rule,  leaves  of  aquatic  and  shade-loving  plants,  as  well 
as  the  leaves  of  most  herbs  have  thinner  walled  epidermal  cells 

59 


LEAF  EPIDERMIS 

1.  Uva-ursi  (Arctostaphylos  uva-ursi,  [L.]  Spring). 

2.  Boldus  (Peumus  boldus,  Molina). 

3.  Catnip  (Nepeta  cataria,  L.)- 

4.  Digitalis  (Digitalis  purpurea,  L.). 
4-A.  Origin  of  hair. 


PLATE  3 


LEAF  EPIDERMIS 

1.  Upper  striated  epidermis  of  chirata  leaf  (Swertia  chirata,  [Roxb.]  Ham.). 

2.  Green  hellebore  leaf  (Veratrum  viride,  Ait.)« 

3.  Bold  us  leaf  (Peumus  boldns,  Molina). 

4.  Under  epidermis  of  India  senna  (Cassia  angustifolia,  Vahl.). 


62  HISTOLOGY   OF   MEDICINAL  PLANTS 

than  have  the  leaves  of  plants  growing  in  soil  under  normal 
conditions,  or  than  have  the  leaves  of  shrubs  and  trees. 

The  widest  possible  range  of  cell-wall  thickness  is  therefore 
found  in  the  medicinal  leaves,  because  the  medicinal  leaves  are 
collected  from  aquatic  plants,  herbs,  shrubs,  trees,  etc. 

The  outer  wall  is  always  thicker  than  the  side  walls.  Even 
the  side  walls  vary  in  thickness  in  some  leaves,  the  wall  next 
to  the  epidermis  being  thicker  than  the  lower  or  innermost 
portion  of  the  wall.  Frequently  the  outermost  part  of  the  side 
walls  is  unequally  thickened.  This  is  the  case  in  the  beaded 
side  walls  characteristic  of  the  epidermis  of  the  leaves  of  laurus, 
myrcia,  boldus,  and  capsicum  seed,  etc.  The  ^  thickness  of  the 
side  walls  of  the  epidermal  cells  of  most  leaves  varies  in  the 
different  leaves. 

In  most  leaves  there  are  five  typical  forms  of  arrangement  of 
epidermal  calls:  First,  those  over  the  veins  which  are  elongated 
in  the  direction  of  the  length  of  the  leaf;  and,  secondly,  those 
on  other  parts  of  the  leaf  which  are  usually  several-sided  and 
not  elongated  in  any  one  direction.  If  the  epidermis  of  the  leaf 
has  stoma,  then  there  is  a  third  type  of  arrangement  of  the 
epidermal  cells  around  the  stoma;  fourthly,  the  cells  surrounding 
the  base  of  hairs;  and  fifthly, '  outgrowths  of  the  epidermis, 
non-glandular  and  glandular  hairs,  etc. 

It  should  be  borne  in  mind  that  in  each  species  of  plant  the 
five  types  of  arrangement  are  characteristic  for  the  species. 

The  character  of  the  outer  wall  of  the  epidermal  cells  differs 
greatly  in  different  plants.  In  most  cases  the  wall  is  smooth; 
senna  is  an  example  of  such  leaves.  In  certain  other  leaves  the 
wall  is  rough,  the  roughness  being  in  the,  form  of  striations. 
In  some  cases  the  striations  occur  in  a  regular  manner;  bella- 
donna leaf  is  typical  of  such  leaves.  In  other  instances  the  wall 
is  striated  in  an  irregular  manner  as  shown  in  chirata  epidermis. 
Very  often  an  epidermis  is  rough,  but  the  roughness  is  not  due 
to  striations.  In  these  cases  the  epidermis  is  unevenly  thickened, 
the  thin  places  appearing  as  slight  depressions,  the  thick  places 
as  slight  elevations.  Boldus  has  a  rough,  but  not  a  striated 
surface. 

Surface  deposits  are  not  of  common  occurrence  in  medicinal 
plants;  waxy  deposits  occur  on  the  stem  of  sumac,  on  a  species 


THE  EPIDERMIS  AND.  PERIDERM  63 

of  raspberry,  on  the  fruit  of  bayberry,  etc.  Resinous  deposits 
occur  on  the  leaves  and  stems  of  grindelia  species,  and  on  yerba 
santa. 

In  certain  leaves  there  are  two  or  three  layers  of  cells  beneath 
the  epidermis  that  are  similar  in  structure  to  the  epidermal  cells. 
These  are  called  hypodermal  cells,  and  they  function  in  the 
same  way  as  the  epidermal  cells. 

Hypodermal  cells  are  very  likely  to  occur  on  the  margin  of 
the  leaf.  Uva-ursi  leaf  has  a  structure  typical  of  leaves  with 
hypodermal  marginal  cells.  Uva-ursi,  like  other  leaves  with 
hypodermal  cells  has  a  greater  number  of  hypodermal  cells 
at  the  leaf  margin  than  at  any  other  part  of  the  leaf 
surface. 

The  cutinized  walls  of  epidermal  cells  are  stained  red  with 
saffranin. 

TESTA  EPIDERMIS 

Testa  epidermal  cells  form  the  epidermal  layers  of  such 
seeds  as  lobelia,  henbane,  capsicum,  paprika,  larkspur,  bella- 
donna, scopola,  etc. 

In  surface  view  the  end  walls  are  thick  and  wavy  in  outline; 
frequently  the  line  of  union — middle  lamella — of  two  cells  is  in- 
dicated by  a  dark  or  light  line,  while  in  others  the  wall  between 
two  cells  appears  as  a  single  wall.  The  walls  are  porous  or 
non-porous,  and  the  color  of  the  wall  varies  from  yellow  to 
brown,  to  colorless.  These  cells  always  occur  in  masses,  com- 
posed partially  of  entire  and  partially  of  broken  fragments. 

In  lobelia  seed  (Plate  4,  Fig.  2)  the  line  of  union  of  adjacent 
cell  walls  appears  as  a  dark  line.  The  walls  are  wavy  in  out- 
line, of  a  yellowish-red  color  and  not  porous. 

In  henbane  seed  (Plate  4,  Fig.  3)  the  line  of  union  between 
the  cells  is  scarcely  visible;  the  walls  are  decidedly  wavy,  more 
so  than  in  lobelia,  and  no  pits  are  visible. 

In  capsicum  seed  (Plate  4,  Fig.  i)  the  cells  are  very  wavy 
and  decidedly  porous,  the  line  of  union  between  the  cell  walls 
being  marked  with  irregular  spaces  and  lines. 

In  belladonna  seed  (Plate  5,  Fig.  i)  the  walls  between  two 
adjacent  cells  are  non-striated  and  non-porous,  and  extremely 
irregular  in  outline. 


PLATE  4 


TESTA  EPIDERMAL  CELLS 

1.  Capsicum  seed  (Capsicum  frutescens,  L.). 

2.  Lobelia  seed  (Lobelia  inflata,  L.). 

3.  Henbane  seed  (Hyoscyamus  niger,  L.). 


PLATE  5 


TESTA  CELLS 

1.  Belladonna  seed  (Atropa  belladonna,  L.). 

2.  Star-aniseed  (Illicium  verum,  Hooker). 

3.  Stramonium  seed  (Datura  stramonium,  L.). 


66  HISTOLOGY   OF   MEDICINAL   PLANTS 

In  star-anise  seed  (Plate  5,  Fig.  2)  the  walls  are  irregularly 
thickened  and  wavy  in  outline. 

In  stramonium  seed  (Plate  5,  Fig.  3)  the  walls  are  very 
thick,  wavy  in  outline,  and  striated. 

PLANT  HAIRS   (TRICHOMES) 

In  histological  work  plant  hairs  are  of  great  importance,  as 
they  offer  a  ready  means  of  distinguishing  and  differentiating 
between  plants,  or  parts  of  plants,  when  they  occur  in  a  broken 
.or  finely  powdered  condition.  There  is  no  other  element  in 
powdered  drugs  which  is  of  so  great  a  diagnostic  value  as  the 
plant  hair.  The  same  plant  will  always  have  the  same  type 
of  hair,  the  only  noticeable  variation  being  in  the  size.  In 
microscopical  drug  analysis  the  presence  of  hairs  is  always  noted, 
and  in  many  cases  the  purity  of  the  powder  can  be  ascertained 
from  the  hairs.  Botanists  seem  to  have  given  little  attention  to 
the  study  of  plant  hairs.  This  accounts  for  the  fact  that  in- 
formation concerning  them  is  very  meagre  in  botanical  literature, 
and,  as  far  as  the  author  can  learn,  no  one  has  attempted  to 
classify  them.  In  systematic  work,  plant  hairs  could  be  used 
to  'great  advantage  in  separating  genera  and  even  species. 
Hairs  are,  of  course,  a  factor  now  in  systematic  work.  The 
lack  of  hairs  is  indicated  by  the  term  glabrous.  Their  presence 
is  indicated  by  such  terms  as  hispid,  villous,  etc.  In  certain 
cases  the  term  indicates  position  of  the  hair  as  ciliate  when  the 
hair  is  marginal.  When  hairs  influence  the  color  of  the  leaf, 
such  terms  as  cinerous  and  canescent  are  used.  In  all  the  cases 
cited  no  mention  is  made  of  the  real  nature  of  the  hair. 

In  systematic  work,  as  in  pharmacognosy,  we  must  work 
with  dried  material,  and  it  is  only  those  hairs  which  retain 
their  form  under  such  conditions  which  are  of  classification 
value. 

Hairs  are  the  most  common  outgrowths  of  the  epidermal 
cells.  They  are  classified  as  glandular  or  non-glandular,  accord- 
ing to  their  structure  and  function.  The  glandular  hairs  will 
be  considered  under  synthetic  tissue. 

Each  group  is  again  subdivided  into  a  number  of  secondary 
groups,  depending  upon  the  number  of  cells  present,  their  form, 


THE  EPIDERMIS  AND  PERIDERM  67 

their  arrangement,  their  size,  their  color,  the  character  of  their 
walls,  whether  rough  or  smooth,  whether  branched  or  non- 
branched,  whether  curved,  twisted,  straight,  or  twisted  and 
straight,  whether  pointed,  blunt,  or  forked. 

FORMS   OF   HAIRS 

PAPILLA 

Papillae  are  epidermal  cells  which  are  extended  outward  in 
the  form  of  small  tubular  outgrowths. 

Papillae  occur  on  the  following  parts  of  the  plant:  flower- 
petals,  stigmas,  styles,  leaves,  stems,  seeds,  and  fruits.  Papillae 
occur  on  only  a  few  of  the  medicinal  leaves. 

The  under  surface  of  both  Truxillo  (Plate  6,  Fig.  3)  and 
Huanuca  coca  have  very  small  papillae.  The  outermost  wall  of 
these  papillae  are  much  thicker  than  the  side  walls.  The  papillae 
of  klip  buchu  (Plate  6,  Fig.  4),  an  adulterant  of  true  buchu,  has 
large  thick- walled  papillae. 

The  velvety  appearance  of  most  flower-petals  (Plate  6, 
Figs.  2  and  5)  is  due  to  the  presence  of  papillae.  The  papillae 
of  flower-petals  are  very  variable.  In  calendula  flowers  (Plate 
6,  Fig.  i)  they  are  small,  yellowish  in  color,  and  the  outer  wall 
is  marked  with  parallel  striations  which  appear  as  small  teeth 
in  cross-section.  The  ray  petal  papillae  of  anthemis  consist  of 
rather  large,  broad,  blunt  papillae  with  slightly  striated  walls. 
The  papillae  of  the  ray  petals  of  the  white  daisy  consist  of  papillae 
which  have  medium  sized,  cone-shaped  papillae  with  finely  striated 
walls.  The  papillae  of  the  flower  stigma  vary  greatly  in  different 
flowers.  In  some  cases  two  or  more  types  of  papillae  occur, 
but  even  in  these  cases  the  papillae  are  characteristic  of  the 
species. 

The  papillae  differ  greatly  in  the  case  of  the  flowers  of  the 
compositae,  where  two  types  of  flowers  are  normally  present — 
namely,  the  ray  flowers  and  the  disk  flowers. 

In  all  cases  observed  the  papillae  of  the  stigma  of  the  ray 
flowers  are  always  smaller  than  the  papillae  of  the  stigma  of  the 
disk  flowers.  It  would  appear  from  extended  observation  that 
the  papillae  of  the  ray  flower  stigma  are  being  gradually  aborted. 
The  papillae  of  the  style  are  always  different  from  the  papillae 


PLATE   6 


PAPILLA 

1.  Calendula  flowers  (Calendula  officinalis,  L.). 

2.  White  daisy  ray  flowe'r  (Chrysanthemum  leucanthemum,  L.). 

3.  Coca  leaf  (Erythroxylon  coca,  Lamarck). 

4.  Klip  buchu. 

5.  Anthemis  ray  petal  (Anthemis  nobilis,  L.). 


THE   EPIDERMIS   AND   PERIDERM  69 

of  the  stigma.     The  style  papillae  are  always  smaller,  and  they 
are  of  a  different  form. 

UNICELLULAR  NON-GLANDULAR  HAIRS 

True  plant  hairs  are  tubular  outgrowths  of  the  epidermal 
cell,  the  length  of  these  outgrowths  being  several  times  the 
width  of  the  hair. 

The  unicellular  hairs  are  common  to  many  plants.  The  two 
groups  of  non-glandular  unicellular  hairs  are,  first,  the  solitary; 
and  secondly,  the  clustered  hairs. 

Solitary  unicellular  hairs  occur  on  the  leaves  of  chestnut, 
yerba  santa,  lobelia,  cannabis  indica,  the  fruit  of  anise,  and 
the  stem  of  allspice,  senna,  and  cowage. 

Chestnut  hairs  (Plate  7,  Fig.  i)  have  smooth  yellowish-colored 
walls,  and  the  cell  cavity  contains  reddish-brown  tannin.  These 
hairs  occur  solitary  or  clustered;  the  clustered  hairs  normally 
occur  on  the  leaf,  but  in  powdering  the  drug,  individual  hairs  of 
the  cluster  become  separated  or  solitary. 

Yerba  santa  hairs  (Plate  7,  Fig.  4)  are  twisted,  the  lumen  or 
cell  cavity  is  very  small,  and  the  walls,  which  are  very  thick, 
are  grayish- white. 

Lobelia  hairs  (Plate  7,  Fig.  5)  are  very  large.  The  walls 
are  grayish-white,  and  the  outer  surface  extends  in  the  form 
of  small  elevations  which  make  the  hair  very  rough.  The  hair 
tapers  gradually  to  a  solid  point. 

Cannabis  indica  hairs  (Plate  7,  Fig.  6)  are  curved.  The 
apex  tapers  to  a  point  and  the  base  is  broad,  and  it  frequently 
contains  deposits  of  calcium  carbonate.  The  walls  are  grayish- 
white  in  appearance,  and  rough.  The  roughness  increases 
toward  the  apex. 

The  hairs  of  anise  (Plate  7,  Fig.  7)  are  mostly  curved;  the 
walls  are  thick,  yellowish- white,  and  the  outer  surface  is  rough; 
this  is  due  to  the  numerous  slight  centrifugal  projections  of  the 
outer  wall. 

Allspice  stem  hairs  (Plate  7,  Fig.  2)  have  smooth  walls. 
The  cell  cavity  is  reddish-brown.  The  hair  is  curved. 

The  hair  of  senna  (Plate  7,  Fig.  10)  is  light  greenish-yellow 
with  rough  papillose  walls.  The  hair  is  usually  curved  and 
tapering,  and  it  does  not  have  any  characteristic  cell  contents. 


PLATE   7 


UNICELLULAR  SOLITARY  HAIRS 

1.  Chestnut  leaf  (Castanea  dentata,  [Marsh]  Borkh). 

2.  Allspice  stems  (Pimento,  officinalis,  Lindl.). 

3.  Cowage. 

4.  Yerba  santa  (Eriodictyon  californicum,  [H.  and  A.]  Greene). 

5.  Lobelia  (Lobelia  inflata,  L-.). 

6.  Cannabis  indica  (Cannabis  saliva,  L.). 

7.  Anise  fruit  (Pimpinella  anisum,  L.). 

8.  Hesperis  matronalis  (Hesperis  matronalis,  L.). 

9.  Galphimia  glauca  (Galphimia  glauca,  Cav.). 
10.  Senna  (Cassia  angustifolia,  Vahl.). 


PLATE  8 


CLUSTERED  UNICELLULAR  HAIRS 
I  and  2.  European  oak  (Quercus  infectoria,  Olivier). 

3.  Kamala  (Mallotus  philippinensis,  [Lam.]  [Muell.]  Arg.). 

4.  Witch-hazel  leaf  (Hamamelis  virginiana,  L.). 

5.  Althea  leaf  (Althcea  officinalis,  L.). 


72  HISTOLOGY   OF   MEDICINAL   PLANTS 

Cowage  hairs  (Plate  7,  Fig.  3)  are  lance-shaped,  and  they 
terminate  in  a  sharp  point.  The  outer  wall  contains  numerous 
recurved  teeth-like  projections.  The  cell  cavity  is  filled  with 
a  reddish-brown  contents  which  are  somewhat  fissured. 

Clustered  unicellular  hairs  occur  on  the  leaves  of  chestnut, 
witch-hazel,  althea,  European  oak,  etc.  In  European  oak  (Plate 
8,  Figs,  i  and  2)  clusters  of  two  and  three  hairs  occur.  The 
walls  are  yellowish- white,  smooth,  and  the  tip  of  the  hair  is  solid. 

In  kamala  (Plate  8,  Fig.  3)  clusters  of  seven  or  more  hairs 
occur;  the  walls  are  yellowish,  and  the  cell  cavity  is  reddish- 
brown.  In  witch-hazel  leaf  (Plate  8,  Fig.  4)  clusters  of  a  variable 
number  of  hairs  occur.  The  hairs,  which  are  of  various  lengths, 
have  yellowish-white,  thick,  smooth  walls,  and  reddish  cell 
contents. 

In  althea  leaf  (Plate  8,  Fig.  5)  the  hairs  are  nearly  straight 
and  the  walls  are  smooth.  The  basal  portions  of  the  hair  are 
strongly  pitted. 

Branched  solitary  unicellular  hairs  occur  on  the  leaves  of 
hesperis  matronalis  (Plate  7,  Fig.  8),  and  on  galphimia  glauca 
(Plate  7,  Fig.  9). 

The  hair  of  hesperis  matronalis  has  smooth  walls,  and  the 
two  branches  grow  out  nearly  parallel  to  the  leaf  surface. 

The  hair  of  galphimia  glauca  has  rough  walls,  and  the  two 
branches  grow  upward  in  a  bifurcating  manner. 

MULTICELLULAR  HAIRS 

Multicellular  hairs  are  divided  into  the  uniseriate  and  the 
multiseriate  hairs.  Both  of  these  groups  are  divided  into  the 
branched  and  the  non-branched  hairs,  as  follows: 

1.  Uniseriate. 

(A)  Non-branched. 

(B)  Branched. 

2.  Multiseriate. 

(4)  Non-branched. 
(B)  Branched. 

Multicellular  uniseriate  non-branched  hairs  occur  on  the 
leaves  of  digitalis,  Western  and  Eastern  skullcap,  peppermint, 
thyme,  yarrow,  arnica  flowers,  and  sumac  fruit. 

Digitalis  hairs  (Plate  9,  Fig.  i)  are  made  up  of   a   varying 


PLATE  9 


MULTICELLULAR   UNISERIATE    NON-BRANCHED    HAIRS 

1.  Digitalis  leaf  (Digitalis  pur  pur  ea,  L.)- 

2.  Arnica  flower  (Arnica  montana,  L.). 

3.  Western  skullcap  plant  (Scutellaria  canescens,  Nutt.)» 

4.  Eastern  skullcap  plant  (Scutellaria  lateriflora,  L.) 

5.  Peppermint  leaf  (Mentha  piperita,  L.). 

6.  Thyme  leaf  (Thymus  vulgaris,  L.). 

7.  Yarrow  flowers  (Achillea  millefolium,  L.). 

8.  Wormwood  leaf  (Artemisia  absinthium,  L.). 

9.  Sumac  fruit  (Rhus  glabra,  L.). 


74  HISTOLOGY   OP   MEDICINAL   PLANTS 

number  of  uniseriate-arranged  cells  of  unequal  length,  frequently 
placed  at  right  angles  to  the  cells  above  and  below;  the  walls 
are  of  a  whitish  color,  and  are  rough  or  smooth. 

Eastern  skullcap  (Plate  9,  Fig.  4)  has  hairs  with  not  more 
than  four  cells;  these  hairs  are  curved,  and  the  walls  are  whitish, 
sometimes  smooth,  but  usually  rough.  In  Western  skullcap 
(Plate  9,  Fig.  3)  the  hairs  have  sometimes  as  many  as  seven 
cells.  The  walls  are  white  and  rough,  and  the  individual  cells 
of  the  hair  are  much  larger  than  are  the  cells  of  the  hairs  of 
true  skullcap. 

Peppermint  (Plate  9,  Fig.  5)  has  from  one  to  eight  cells. 
The  hair  is  curved,  and  the  walls  are  very  rough. 

Thyme  (Plate  9,  Fig.  6)  has  short,  thick,  rough-walled 
trichomes,  the  terminal  cell  usually  being  bent  at  nearly  right 
angles  to  the  other  cells. 

.  Yarrow  hairs  (Plate  9,  Fig.  7)  have  a  variable  number  of 
cells.  In  all  the  hairs  the  basal  cells  are  short  and  broad,  while 
the  terminal  cell  is  greatly  elongated. 

Arnica  hairs  (one  form,  Plate  9,  Fig.  2)  have  frequently  as 
many  as  four  cells,  the  terminal  cell  being  longer  than  the  basal 
cells.  The  walls  are  white  and  smooth. 

Sumac-fruit  hairs  (Plate  9,  Fig.  9)  have  spindle-shaped, 
reddish-colored  hairs. 

Multicellular  multiseriate  non-branched  hairs  occur  on 
cumin  fruit  and  on  the  tubular  part  of  the  corolla  of  calendula. 

The  hairs  on  cumin  fruit  vary  considerably  in  size.  All  the 
hairs  are  spreading  at  the  base  and  blunt  or  rounded  at  the  apex. 
The  cells  forming  the  hair  are  narrow  and  the  walls  are  thick. 
Three  differently  sized  hairs  are  shown  in  Plate  10,  Fig.  i. 

The  hairs  of  the  base  of  the  ligulate  petals  of  calendula 
(Plate  10,  Fig.  2)  are  biseriate.  The  hairs  are  very  long  and 
the  walls  are  very  thin. 

Multicellular  uniseriate  branched  hairs  occur  on  the  leaves 
of  dittany  of  Crete,  mullen,  and  on  the  calyx  of  lavender  flowers. 

The  dittany  of  Crete  (Plate  n,  Fig.  3)  hair  is  smooth-walled, 
and  the  branches  are  alternate. 

In  mullen  (Plate  n,  Fig.  i)  the  hairs  have  whorled  branches, 
the  walls  are  smooth,  and  the  cell  cavity  usually  contains  air. 

The  lavender  hairs  (Plate  n,  Fig.  2)  have  mostly  opposite 


PLATE    10 


MULTICELLULAR    MULTISERIATE    NON-BRANCHED   HAIRS 

1.  Cumin  (Cuminum  cyminum,  L.)« 

2.  Marigold  (Calendula  qfficinalis,  L.). 


PLATE    ii 


MULTICELLULAR    UNISERIATE    BRANCHED   HAIRS 

1.  Mullen  leaf  (Verbascum  thapsus,  L.). 

2.  Lavender  flowers  (Lavandula  vera,  D.  C.). 

3.  Dittany  of  Crete  (Origanum  dictamnus,  L.). 


THE   EPIDERMIS    AND    PERIDERM  77 

branches,  and  the  walls  are  rough.  Thus  the  multicellular 
branched  hairs  may  be  divided  into  subgroups  which  have 
alternate,  opposite,  whorled,  or  in  certain  hairs  irregularly  ar- 
ranged branches.  Each  class  may  be  again  subdivided  accord- 
ing to  color,  character  of  cell  termination,  etc.,  as  cited  at  the 
beginning  of  the  chapter. 

Occasionally  multicellular  hairs  assume  the  form  of  a  shield 
(Plate  12,  Fig.  i);  in  such  cases  the  hair  is  termed  peltate,  as  in 
the  non-glandular  multicellular  hair  of  shepherdia  canadensis. 

Hairs  grow  out  from  the  surface  of  the  epidermis  in  a  per- 
pendicular, a  parallel,  or  in  an  oblique  direction.  Hairs  which 
grow  parallel  or  oblique  to  the  surface  are  usually  curved,  and 
the  outer  curved  part  of  the  wall  is  usually  thicker  than  the 
inner  curved  wall. 

The  mature  hairs  of  some  plants  consist  of  dead  cells.  In 
other  plants  the  cells  forming  the  hair  are  living.  When  dried, 
those  hairs,  which  were  dead  before  drying,  contain  air;  while 
those  hairs  which  were  living  before  drying,  show  great  variation 
in  color  and  in  the  nature  of  the  cell  contents.  The  contents 
are  either  organic  or  inorganic.  The  commonest  organic  con- 
stituent is  dried  protoplasm.  In  cannabis  indica  are  de- 
posits of  calcium  carbonate. 

Multicellular  multiseriate  branched  hairs  are  the  ultimate 
division  of  the  pappus  of  erigeron,  aromatic  goldenrod,  arnica, 
grindelia,  boneset,  and  life-everlasting. 

The  hairs  of  erigeron  (Plate  13,  Figs.,  i  and  2)  are  slender; 
the  walls  are  porous.  Each  hair  terminates  in  two  cells,  which 
are  greatly  extended  and  sharp-pointed;  the  branches  from  the 
basal  part  of  the  hairs  (Plate  13,  Fig.  i)  are  of  about  the  same 
length  as  the  apical  branches. 

The  hairs  of  aromatic  goldenrod  (Plate  13,  Figs.  3  and  4)  are 
larger  than  those  of  erigeron;  the  diameter  is  greater  and  the 
walls  are  non-porous.  The  apex  of  the  hair  terminates  in  a 
group  of  about  four  cells  of  unequal  length,  which  are  sharp- 
pointed.  The  branches  of  the  basal  cells  (Plate  13,  Fig.  3)  are 
similar  to  the  branches  of  the  apical  cells. 

The  hairs  of  arnica  (Plate  14,  Figs,  i  and  2)  have  thick, 
strongly  porous  walls;  the  branches  terminate  in  sharp  points. 
The  apex  of  the  hair  terminates  in  a  single  cell.  The  basal 


PLATE   12 


NON-GLANDULAR  MULTICELLULAR  HAIRS 
Shepherdia  canadensis,  [L.]  Nutt. 


PLATE   13 


MULTICELLULAR   MULTISERIATE    BRANCHED   HAIRS 

1.  Basal  hairs  of  erigeron  (Erigeron  canadensis,  L.). 

2.  Apical  hairs  of  erigeron  (Erigeron  canadensis,  L.). 

3.  Basal  hairs  of  aromatic  goldenrod  (Solidago  odora,  Ait.)- 

4.  Apical  hairs  of  aromatic  goldenrod  (Solidago  odora,  Ait.). 


80  HISTOLOGY   OF  MEDICINAL  PLANTS 

branches  (Plate  14,  Fig.  2)  are  much  longer  than  special 
branches. 

The  hair  of  grindelia  (Plate  14,  Figs.  3  and  4)  has  very  thick 
walls  with  numerous  elongated  pores.  The  apex  of  the  hair 
terminates  in  a  cluster  of  cells  with  short,  free,  sharp-pointed 
ends.  The  basal  branches  (Plate  14,  Fig.  4)  are  longer  than 
the  apical  branches. 

Boneset  hair  (Plate  15,  Figs,  i  and  2)  has  non-porous  walls. 
The  apex  of  the  hair  terminates  in  two  blunt-pointed  cells. 
The  terminal  wall  is  thicker  than  the  side  wall.  Some  of  the 
branches  lower  down  terminate  in  cells  with  very  thick  or  solid 
points.  The  basal  branches  (Plate  15,  Fig.  i)  are  longer,  but 
the  cells  are  narrower  and  more  strongly  tapering  than  are  the 
branches  of  the  apical  part  of  the  hair. 

Life-everlasting  (Plate  15,  Figs.  3  and  4)  has  uniformly 
thickened  but  non-porous  walls.  The  hair  terminates  in  two 
blunt-pointed,  greatly  elongated  cells. 

The  basal  branches  (Plate  15,  Fig.  4)  are  narrower,  slightly 
tapering,  and  the  base  of  the  branches  frequently  curve  down- 
ward. 

The  cell  cavities  of  these  hairs  are  filled  with  air. 

The  walls  of  hairs  are  composed  of  cutin,  of  lignin,  and 
of  cellulose. 

PERIDERM 

The  periderm  is  the  outer  protective  covering  of  the  stems 
and  roots  of  mature  shrubs  and  trees.  The  periderm  replaces 
the  epidermis.  The  periderm  may  be  composed  of  cork  cells, 
stone  cell-cork,  or  a  mixture  of  cork,  parenchyma,  fibres,  stone 
cells,  etc. 

CORK  PERIDERM 

The  typical  periderm  is  made  up  of  cork  cells.  Cork  cells 
vary  in  appearance,  according  to  the  part  of  the  cell  viewed. 

On  surface  view  (Plate  16,  Fig.  A)  the  cork  cells  are  angled 
in  outline  and  are  made  up  of  from  four  to  seven  side  walls; 
five-  and  six-sided  cells  are  more  common  than  the  four-  and 
seven-sided  cells.  Surface  sections  of  cork  cells  show  their 


MULTICELLULAR   MULTISERIATE    BRANCHED   HAIRS 

1.  Apical  hairs  arnica  (Arnica  montana,  L.). 

2.  Basal  hairs  arnica  (Arnica  montana,  L.). 

3.  Apical  hairs  grindelia  (Grindelia  squarrosa,  [Pursh]  Dunal). 

4.  Basal  hairs  grindelia  (Grindelia  squarrosa,  [Pursh]  Dunal). 


PLATE   15 


MULTICELLULAR    MULTI SERIATE    BRANCHED   HAIRS 

1.  Apical  hairs  boneset  (Eupatorium  perfoliatum,  L.). 

2.  Basal  hairs  boneset  (Eupatorium  perfoliatum,  L.). 

3.  Apical  hairs  life-everlasting  (Gnaphalium  obtusifolium,  L.). 

4.  Basal  hairs  life-everlasting  (Gnaphalium  obtusifolium,  L.). 


THE  EPIDERMIS   AND  PERIDERM  83 

length  and  width.  These  side  walls  usually  appear  nearly  white, 
while  the  end  wall,  particularly  of  the  outermost  cork  cells, 
usually  appears  brown  or  reddish-brown,  or  in  some  cases  nearly 
black. 

Cork  cells  on  cross-section  are  rectangular  in  form,  and  they 
are  arranged  in  superimposed  rows,  the  number  of  rows  being 
gradually  increased  as  the  plant  grows  older.  Such  an  increase 
in  the  number  of  rows  of  cork  cells  is  shown  in  the  cross-section 
of  cascara  sagrada  (Plate  16,  Fig.  C). 

Cork  cells  fit  together  so  closely  that  there  is  no  intercellular 
spaces  between  the  cells.  In  this  case  two  rows  of  cork  cells 
occupy  no  greater  space  than  the  solitary  row  of  cork  cells 
immediately  over  .and  external  to  them.  As  a  rule,  the  outer- 
most layers  of  cork  cells  have  a  narrower  radial  diameter  than 
the  cork  cells  of  the  underlying  layers.  This  is  due  to  the  fact 
that  these  outer  cells  are  stretched  as  the  stem  increases  in 
diameter.  This  view  shows  the  height  of  cork  cells,  but  not 
always  the  length,  which  will,  of  course,  vary  according  to  the 
part  of  the  cell  cut  across.  In  a  section  a  few  millimeters  in 
diameter,  however,  all  the  variations  in  size  may  be  observed. 
The  color  of  the  walls  is  nearly  white. 

The  cavity  may  contain  tannin  or  other  substances.  When 
tannin  is  present,  the  cavity  is  of  a  brownish  or  brownish-red 
color,  or  it  may  be  nearly  black.  Most  barks  appear  devoid  of 
any  colored  or  colorless  cell  contents. 

The  radial  section  (Plate  16,  Fig.  B)  of  cork  cells  shows  the 
height  of  the  cells  and  the  width  of  the  cells  at  the  point  cut 
across.  Some  cells  will  be  cut  across  their  longest  diameter,  while 
others  will  be  cut  across  their  shortest  diameter.  Cork  cells  are, 
therefore,  smaller  in  radial  section  than  they  are  in  cross-section. 
The  color  of  the  walls  is  white,  and  the  color  and  nature  of  the 
cell  contents  vary  for  the  same  reasons  that  they  vary  in 
cross-sections. 

The  number  of  layers  of  cork  cells  occurring  in  cross-  and 
radial-sections  varies  according  to  the  age  of  the  plant,  to  the  type 
of  plant,  and  to  the  conditions  under  which  the  plant  is  growing. 

The  number  of  layers  of  cork  cells  is  not  of  diagnostic  im- 
portance, nor  is  the  surface  view  of  cork  cells  diagnostic  except 
in  certain  isolated  cases. 


PLATE   16 


PERIDERM  OF  CASCARA  SAGRADA  (Rhamnus  purshiana,  D.C.) 

A.  I,  Outline  of  cork  cells;  2,  Line  of  contact  of  adjoining  cork  cells. 

B.  Radial  longitudinal  section  of  cascara  sagrada.     i,  Cork  cells;  2,Phel- 
logen;  3,  Forming  parenchyma  cells;  4,  Cortical  parenchyma  cells. 

C.  Cross-section  of  cascara  sagrada.     I,  Cork  cells;  2,  Phellogen;  3,  Form- 
ing parenchyma  cells;  4,  Cortical  parenchyma  cells. 


THE  EPIDERMIS  AND   PERIDERM  85 

The  presence  or  absence  of  cork  or  epidermal  tissue  in  pow- 
ders must  always  be  noted.  The  presence  of  cork  enables  one  to 
distinguish  Spanish  from  Russian  licorice.  In  like  manner,  the 
presence  of  epidermis  enables  one  to  distinguish  the  pharma- 
copceial  from  the  unofficial  peeled  calamus.  The  absence  of 
epidermis  in  Jamaica  ginger  is  one  of  the  means  by  which  this 
variety  is  distinguished  from  the  other  varieties  of  ginger,  etc. 

In  canella  alba  the  periderm  is  replaced  by  stone  cell-cork. 
That  is,  the  cells  forming  the  periderm  are  of  a  typical  cork 
shape,  but  the  walls  are  lignified,  unequally  thickened,  and 
the  inner  or  thicker  walls  are  strongly  porous,  and  the  walls 
are  of  a  yellowish  color.  Stone  cell-cork  forms  the  periderm 
of  clove  bark  also,  but  the  cells  are  narrower  and  longer,  and 
the  inner  wall  is  not  so  thick  or  porous  as  is  the  case  in  canella 
alba  bark. 

STONE  CELL  PERIDERM 

In  canella  alba  (Plate  17,  Fig.  B)  cork  periderm  is  frequently 
replaced  by  stone  cells,  particularly  in  the  older  barks.  These 
stone  cells  form  the  periderm  because  they  replace  the  cork 
periderm,  which  fissures  and  scales  off  as  the  root  increases 
in  diameter. 

•The  side  and  end  walls  of  cork  cells  are  of  nearly  uniform 
diameter.  Exceptions  occur,  but  they  are  not  common.  In 
buchu  stem  (Plate  101,  Fig.  3),  the  cork  cells  have  thick  outer 
walls,  but  thin  sides  and  inner  walls.  The  cell  cavity  contains 
reddish-brown  deposits  of  tannin. 

PARENCHYMA  AND   STONE  CELL  PERIDERM 

As  the  trees  and  shrubs  increase  in  diameter,  cracks  or  fis- 
sures occur  in  the  periderm,  or  corky  layer.  In  such  cases  the 
phellogen  cells  divide  and  redivide  in  such  manner  as  to  cut 
off  a  portion  of  the  parenchyma  cells,  stone  cells,  and  fibres  of 
the  cortex  which  is  inside  of  and  below  the  fissure.  All  the 
parenchyma  cells,  etc.,  exterior  to  the  newly  formed  cork  cells 
soon  lose  their  living-cell  contents,  since  their  food-supply  is 
cut  off  by  the  impervious  walls  of  the  cork  cells.  In  time  they 
are  forced  outward  by  the  developing  cork  cells  until  they 


PLATE   17 


A.  Cross-section  of  Mandrake  Rhizome  (Podophyllum  peltatum,  L.). 

1.  Epidermis. 

2.  Phellogen. 

3.  Cortical  parenchyma. 

B.  Stone  cell  periderm  of  white  cinnamon  (Canetta  alba,  Murr.). 


PLATE  1 8 


(T 

i_J     i 


CO 


88  HISTOLOGY   OF  MEDICINAL  PLANTS 

partially  or  completely  fill  the  break  in  the  periderm.  In  white 
oak  bark  (Plate  18),  as  in  other  barks,  a  large  part  of  the  peri- 
derm  is  composed  of  dead  and  discolored  cortical  cells. 

ORIGIN  OF  CORK  CELLS 

The  cork  cells  are  formed  by  the  meristimatic  phellogen 
cells,  which  originate  from  cortical  parenchyma.  These  cells 
divide  into  two  cells,  the  outer  changing  into  a  cork  cell,  while 
the  inner  cell  remains  meristimatic.  In  other  instances  the 
outer  cell  remains  meristimatic,  while  the  inner  cell  changes 
into  a  cortical  parenchyma  cell.  The  development  of  a  cortical 
parenchyma  cell  from  a  divided  phellogen  cell  is  shown  in  Plate 
101,  Fig.  6.  Both  the  primary  and  secondary  cork  cells  originate 
from  the  phellogen  or  cork  cambrium  layer.  Cork'  cells  do  not 
contain  living-cell  contents;  in  fact,  in  the  majority  of  medicinal 
barks  the  cork  cells  contain  only  air. 

The  walls  of  typical  cork  cells  are  composed,  at  least  in  part, 
of  suberin,  a  substance  which  is  impervious  to  water  and  gases. 
In  certain  cases  layers  of  cellulose,  lignin,  and  suberin  have  been 
identified.  Suberin,  however,  is  present  in  all  cork  cells,  and 
in  some  cases  all  of  the  walls  of  cork  cells  are  composed  of  suberin. 

Suberized  cork  cells  are  colored  yellow  with  strong  sodium 
hydroxide  solutions  and  by  chlorzinciodide. 


CHAPTER  III 

MECHANICAL  TISSUES 

The  mechanical  tissues  of  the  plant  form  the  framework 
around  which  the  plant  body  is  built  up.  These  tissues  are 
constructed  and  placed  in  such  a  manner  in  the  different  organs 
of  the  plant  as  to  meet  the  mechanical  needs  of  the  organ.  Many 
underground  stems  and  roots  which  are  subjected  to  radial  pres- 
sure have  the  hypodermal  and  endodermal  cells  arranged  in  the 
form  of  a  non-compressible  cylinder.  Such  an  arrangement  is 
seen  in  sarsaparilla  root  (Plate  38,  Fig.  4).  The  mechanical 
tissue  of  the  stem  is  arranged  in  the  form  of  solid  or  hollow 
columns  in  order  to  sustain  the  enormous  weight  of  the  branches. 
In  roots  the  mechanical  tissue  is  combined  in  ropelike  strands, 
thereby  effectively  resisting  pulling  stresses.  The  epidermis  of 
leaves  subjected  to  the  tearing  force  of  the  wind  has  epidermal 
cells  with  greatly  thickened  walls,  particularly  at  the  margin  of 
the  leaf.  The  epidermal  cells  of  most  seeds  have  very  thick 
and  lignified  cell  walls,  which  effectively  resist  crushing  forces. 

The  cells  forming  mechanical  tissues  are:  bast  fibres,  wood 
fibres,  collenchyma  cells,  stone  cells,  testa  epidermal  cells,  and 
hypodermal  and  endodermal  cells  of  certain  plants.  The  walls 
of  the  cells  forming  mechanical  tissues  are  thick  and  lignified, 
with  the  exception  of  the  collenchyma  cells  and  a  few  of  the 
fibres.  Lignified  cells  are  as  resistive  to  pulling  and  other 
stresses  as  similar  sized  fragments  of  steel.  The  hardness  of 
their  wall  and  their  resistance  to  crushing  explain  the  fact  that 
they  usually  retain  their  form  in  powdered  drugs  and  foods. 

BAST  FIBRES 

One  of  the  most  important  characters  to  be  kept  in  mind  in 
studying  bast  fibres  is  the  structure  of  the  wall.  In  fact,  the 
author's  classification  of  bast  fibres  is  based  largely  on  wall 

89 


90  HISTOLOGY   OF  MEDICINAL  PLANTS 

structure.  Such  a  classification  is  logical  and  accurate,  because 
it  is  based  upon  permanent  characters.  Another  character  used 
in  classifying  bast  fibres  is  the  nature  of  the  cell,  whether  branched 
or  non-branched.  In  fact,  this  latter  character  is  used  to  separate 
all  bast  fibres  into  two  fundamental  groups — namely,  branched 
bast  fibres  and  non-branched  bast  fibres.  The  third  important 
character  utilized  in  classifying  fibres  is  the  presence  or  absence 
of  crystals. 

Bast  fibres  are  classified  as  follows: 

1 .  Crystal  bearing. 

2.  Non-crystal  bearing. 

The  crystal-bearing  fibres  are  divided  into  two  classes: 

1.  Of  leaves. 

2.  Of  barks. 

The  non-crystal  bearing  are  divided  into : 

1.  Branched. 

2.  Non-branched. 

The  branched  and  non-branched  are  divided  into  four  classes : 

1 .  Non-porous  and  non-striated. 

2.  Porous  and  non-striated. 

3.  Striated  and  non-porous. 

4.  Porous  and  striated. 

CRYSTAL-BEARING   BAST   FIBRES 

The  crystal-bearing  fibres  are  composed  (i)  of  groups  of 
fibres,  (2)  of  crystal  cells,  and  (3)  of  crystals.  In  these  cases 
the  groups  of  fibres  are  large,  and  they  are  frequently  completely 
covered  by  crystal  cells,  which  may  or  may  not  contain  a  crystal. 
The  crystals  found  on  the  fibres  from  the  different  plants  vary 
considerably  in  size  and  form.  As  a  rule,  the  fibres  when  sepa- 
rated are  free  of  crystal  cells  and  crystals.  This  is  so  because 
the  crystal  cells  are  exterior  to  the  fibres,  and  in  separating  the 
fibres  during  the  milling  process  the  crystal  cells  are  broken  down 
and  removed  from  the  fibres.  It  is  common,  therefore,  to  find 
isolated  fibres  and  crystals  associated  with  the  crystal-bearing 
fibres.  The  fibres  which  are  crystal-bearing  may  be  striated 
or  porous,  etc.;  but  owing  to  the  fact  that  the  grouping  of  the 
fibres  and  crystals  is  so  characteristic,  little  or  no  attention  is 
paid  to  the  structure  of  the  individual  fibres. 


I 'LATE    19 


CRYSTAL-BEARING  FIBRES  CK  BARKS 

1.  Frangula  (Rhamnus  frangula,  L.)- 

2.  Cascara  sagrada  (Rhamnus  pur  ski-ana,  D.C.). 

3.  Spanish  licorice  (Glycyrrhiza  glabra,  L.). 

4.  Witch-hazel  bark  (Ilamamdis  virginiana,  L.). 


92  HISTOLOGY   OF  MEDICINAL  PLANTS 

Crystal-bearing  fibres  occur  in  the  barks  of  frangula  (Plate 
19,  Fig.  i);  cascara  sagrada  (Plate  19,  Fig.  2);  witch-hazel 
(Plate  19,  Fig.  4);  in  cocillana  (Plate  20,  Fig.  i);  in  white  oak 
(Plate  20,  Fig.  2);  in  quebracho  (Plate  20,  Fig.  3);  and  in 
Spanish  licorice  root  (Plate  19,  Fig.  3). 

The  crystal-bearing  fibres  of  leaves  are  always  associated 
with  vessels  or  tracheids  and  with  cells  with  chlorophyl.  The 
presence  or  absence  of  crystal-bearing  fibres  in  leaves  should 
always  be  noted.  The  crystal-bearing  fibres  of  leaves  are 
composed  of  fragments  of  conducting  cells,  fibres,  crystal  cells, 
and  crystals.  The  crystal-bearing  fibres  of  leaves  occur  in 
larger  fragments  than  the  other  parts  of  the  leaf,  because  the 
fibres  are  more  resistant  to  powdering.  Having  observed  that 
a  leaf  has  crystal-bearing  fibres,  in  order  to  identify  the  powder 
it  is  necessary  to  locate  one  of  the  other  diagnostic  elements 
of  the  leaf — as  the  papillae  of  coca  (Plate  21,  Fig.  i),  or  the  hair 
of  senna  (Plate  21,  Fig.  3),  or  the  vessels  in  eucalyptus  (Plate  21, 
Fig.  2). 

Branched  bast  fibres  occur  in  only  a  few  of  the  medicinal 
plants,  notable  examples  being  tonga  root  and  sassafras  root. 
Occasionally  one  is  found  in  mezereum  bark. 

The  bast  fibre  of  tonga  root  (Plate  22,  Fig.  2)  often  has  seven 
branches,  but  four-  and  five-branched  forrns  are  more  common. 
The  walls  are  non-porous,  non-striated,  and  nearly  white. 

The  bast  fibre  of  sassafras  (Plate  22,  Fig.  i)  has  thick,  non- 
porous,  and  non-striated  walls,  and  the  branching  occurs  usually 
at  one  end  only  of  the  fibre.  Most  of  the  bast  fibres  of  sassafras 
root  are  non-branched. 

POROUS  AND   STRIATED  BAST  FIBRES 

Porous  and  striated  walled  bast  fibres  occur  in  blackberry 
bark  of  root,  wild-cherry  bark,  and  in  cinchona  bark. 

The  fibres  of  blackberry  root  bark  (Plate  23,  Fig.  i)  have 
distinctly  porous  and  striated  walls;  the  cavity,  which  is  usually 
greater  than  the  diameter  of  the  wall,  contains  starch.  These 
fibres  usually  occur  as  fragments. 

In  wild-cherry  bark  (Plate  23,  Fig.  2)  the  fibre  has  short, 
thick,  unequally  thickened  walls,  which  are  porous  and  striated. 
Most  of  the  fibres  are  unbroken. 


PLATE  20 


CRYSTAL-BEARING  FIBRES  OF  BARKS 

1.  Cocillana  (Guarea  rusbyi,  [Britton]  Rusby). 

2.  White  oak  (Quercus  alba,  L.). 

3.  Quebracho  (Aspidosperma  quebracho-bianco,  Schlechtendal). 


PLATE   21 


CRYSTAL-BEARING  FIBRES  OF  LKAVI-.S 

1.  Coca  leaf  (Erythroxylon  coca,  Lam.). 

2.  Eucalyptus  leaf  (r.-m  ah  f>tns  f>lobnlns,  Lahill). 

3.  Senna  leaf  (Cassia  aiiguxtifolia,  \'ahl.). 


PLATE  22 


BRANCHED  BAST  FIBRES 

1.  Sassafras  root  bark  (Sassafras  variifolium,  [Salisb.]  Kuntze). 

2.  Tonga  root. 


96  HISTOLOGY  OF  MEDICINAL  PLANTS 

Yellow  cinchona  bark  (Plate  23,  Fig.  3)  has  very  thick, 
prominently  striated  porous-walled  fibres,  with  either  blunt  or 
pointed  ends.  The  cavity  is  narrow,  and  the  pores  are  simple 
or  branched. 

POROUS  AND  NON-STRIATED  BAST  FIBRES 

Porous  and  non-striated  bast  fibres  occur  in  marshmallow 
root  and  echinacea  root. 

The  fibres  of  marshmallow  (Plate  24,  Fig.  3)  usually  occur 
in  fragments.  The  walls  have  simple  pores,  and  the  diameter 
of  the  cell  cavity  is  very  wide;  the  pores  on  the  upper  or  lower 
wall  are  circular  or  oval  in  outline  (end  view). 

The  bast  fibres  of  echinacea  root  (Plate  24,  Fig.  4)  are  seldom 
broken;  the  walls  are  yellow,  the  pores  are  simple  and  numerous. 
The  edges  and  surface  of  the  fibres  are*  frequently  covered  with 
a  black  intercellular  substance. 

NON-POROUS  AND   STRIATED  BAST  FIBRES 

Non-porous  and  striated  bast  fibres  occur  in  elm  bark, 
stillingia  root,  and  cundurango  bark.  The  bast  fibres  of  elm 
bark  (Plate  25,  Fig.  i)  occur  in  broken,  curved,  or  twisted  frag- 
ments. The  central  cavity  is  very  small,  and  the  walls  are 
longitudinally  striated. 

In  powdered  stillingia  root  (Plate  25,  Fig.  2)  the  bast  fibres 
are  broken,  and  the  wall  is  very  thick  and  longitudinally  striated. 
The  central  cavity  is  small  and  usually  not  visible.  Bast  fibres 
of  cundurango  (Plate  25,  Fig.  3)  are  broken  in  the  powder. 
The  cavity  is  very  narrow,  and  the  striations  are  arranged 
spirally,  less  frequently  transversely.  - 

NON-POROUS  AND   NON-STRIATED  BAST  FIBRES 

Non-porous  and  non-striated  walled  bast  fibres  occur  in 
mezereum  bark,  in  Ceylon  cinnamon,  in  sassafras  root  bark, 
and  in  soap  bark. 

The  simplest  non-porous  and  non-striated  walled  bast  fibres 
are  found  in  mezereum  bark  (Plate  26,  Fig.  4).  The  individual 
fibre  is  very  long.  If  often  measures  over  three  millimeters  in 
length,  so  that  in  the  powder  the  fibre  is  usually  broken.  The 
wall  is  non-lignified,  white,  non-porous,  and  of  uniform  diameter. 


PLATE  23 


POROUS  AND  STRIATED  BAST  FIBRES 

1.  Blackberry  root  (Rubus  cuneifolius,  Pursh.). 

2.  Wild  cherry  (Prunus  serotina,  Ehrh.). 

3.  Yellow  cinchona  (Cinchona  species). 


PLATE   24 


POROUS  AND  NON-STRIATED  BAST  FIHRKS 


1.  Sarsaparilla  root  (Hypoderm),  (Smilax  officinalis,  Kunth). 

2.  I'nicorn  root  (EndodermJ. 

3.  Marshmallow  root  (Althcea  officinalis,  L.)« 

4.  Echinacea  root  (Echinarra  an^itsfifolia,  D.  C.), 


PLATE   25 


NON-POROUS    AND   STRIATED    BAST   FIBRES 

1.  Elm  bark  (Ulmus  fulva,  Michaux). 

2.  Stillingia  root  (Stillingia  sylvatica,  L.). 

3.  Cundurango  root  bark  (Marsdenia  cundurango,  [Triana]  Nichols). 


100  HISTOLOGY  OF  MEDICINAL  PLANTS 

In  Ceylon  cinnamon  (Plate  26,  Fig.  2)  the  bast  fibres  measure 
up  to  .900  mm.  in  length,  so  that  in  powdering  the  bark  the 
fibre  is  rarely  broken.  These  bast  fibres,  unlike  the  bast  fibres 
of  mezereum,  have  thick,  white  walls  and  a  narrow  cell  cavity. 
Both  ends  of  the  fibre  taper  gradually  to  a  long,  narrow  point. 

In  Saigon  cinnamon  the  bast  fibres  are  not  as  numerous 
as  they  are  in  Ceylon  cinnamon.  The  individual  fibres  are 
thicker  than  in  Ceylon  cinnamon,  and  the  walls  are  yellowish 
and  rough  and  the  ends  bluntly  pointed.  These  fibres  are  rarely 
ever  free  from  adhering  fragments  of  parenchyma  tissue. 

In  sassafras  root  bark  (Plate  26,  Fig.  3)  the  fibre  has  one 
nearly  straight  side — the  side  in  contact  with  the  other  bast 
fibres — and  an  outer  side  with  a  wavy  outline,  caused  by  the 
fibre's  pressing  against  parenchyma  cells,  the  point  of  highest 
elevation  being  the  point  of  the  fibre's  growth  into-  the  inter- 
cellular space  between  two  cells.  The  outer  part  of  the  wall 
tapers  gradually  at  either  end  to  a  sharp  point.  The  walls 
are  white,  thick,  and  non-porous. 

In  soap  bark  (Plate  26,  Fig.  i)  the  bast  fibres  have  thick, 
white,  wavy  walls  and  a  narrow  cavity.  One  end  of  the  cell  is 
frequently  somewhat  blunt  while  the  opposite  end  is  slightly 
tapering. 

The  branched  stone  cells  of  wild-cherry  bark  have  three  or 
more  branches.  The  pores  are  small  and  usually  non-branched, 
and  the  striations  are  very  fine  and  difficult  to  see  unless  the 
iris  diaphragm  is  nearly  closed.  The  central  cavity  is  very 
narrow  and  frequently  contains  brown  tannin. 

The  branched  stone  cells  of  hemlock  bark  are  very  large; 
the  walls  are  white  and  distinctly  porous  bordering  on  the  cell 
cavity,  which  contains  bright  reddish-brown  masses  of  tannin. 

In  cross-section  bast  fibres  occur  singly  or  isolated,  as  in 
Saigon  cinnamon  (Plate  34,  Fig.  i);  or  in  groups,  as  in  meni- 
spermum  (Plate  27,  Figs,  i  and  2);  or  in  the  form  of  continuous 
bands,  as  in  buchu  stem  (Plate  100,  Fig.  5). 

Bast  fibres  are  seen  in  longitudinal  view  in  powdered  drugs. 
The  cell  cavity  shows  throughout  the  length  of  the  fibre.  This 
cavity  differs  greatly  in  different  fibres.  In  soap  bark  (Plate 
26,  Fig.  i)  there  is  scarcely  any  cell  cavity,  while  in  mezereum 
bark  (Plate  26,  Fig.  4)  the  cell  cavity  is  very  large. 


PLATE   26 


NON-POROUS   AND    NON-STRIATED    BAST  FIBRES 

1.  Soap  bark  (Quillaja  saponaria,  Molina). 

2.  Ceylon  cinnamon  bark  (Cinnamomum  zeylanicum,  Nees). 

3.  Sassafras  root  bark  (Sassafras  variifolium,  [Salisb.]  Kuntze). 
|.  Mezereum  bark  (Daphne  mezereum,  L.). 


PLATE   27 


GROUPS  OF  BAST  FIBRES 

1.  Menispermum  rhizome  (Menispsrmum  canadensis,  L.). 

2.  Althea  root  (AlthcBa  officinalis,  L.)  showing  two  groups  of  bast  fibres. 


MECHANICAL   TISSUES  103 

The  pores,  which  are  absent  in  many  drugs,  are,  when 
present,  either  simple,  as  in  echinacea  root  (Plate  24,  Fig.  4), 
or  they  are  branched,  as  in  yellow  cinchona  (Plate  23,  Fig.  3). 

In  each  of  the  above  fibres  the  length  and  width  of  the 
fibre  are  shown.  The  fibres  also  have  pores  of  variable  length. 
Such  a  variation  is  common  to  most  fibres  with  pores.  That 
part  of  the  wall  immediately  over  or  below  the  cell  cavity  shows 
the  end  view  or  diameter  of  the  pore,  as  in  the  fibre  of  marsh- 
mallow  root  (Plate  24,  Fig.  3).  As  a  rule,  however,  the  pores 
show  indistinctly  on  the  upper  and  lower  wall. 

OCCURRENCE  IN  POWDERED  DRUGS 

In  powdered  drugs  bast  fibres  occur  singly  or  in  groups. 
The  individual  fibres  may  be  broken,  as  in  mezereum  and  elm 
bark,  or  they  may  be  entire,  as  in  Ceylon  cinnamon  and  in 
sassafras  bark  (Plate  26,  Figs.  2  and  3). 

The  lignified  walls  of  bast  fibres  are  colored  red  by  a  solution 
of  phlorogucin  and  hydrochloric  acid,  and  the  walls  are  stained 
yellow  by  aniline  chloride. 

In  fact,  few  of  the  fibres  found  in  individual  plants  occur 
in  a  broken  condition. 

Isolated  bast  fibres  are  circular  in  outline.  Bast  fibres,  when 
forming  part  of  a  bundle,  have  angled  outlines  when  they  are 
completely  surrounded  by  other  bast  fibres;  but  when  they 
occur  on  the  outer  part  of  the  bundle,  and  when  in  contact  with 
parenchyma  or  other  cortical  cells,  they  are  partly  angled  and 
partly  undulated  in  outline. 

In  the  bast  fibres  the  pores  are  placed  at  right  angles  to 
the  length  of  the  fibre.  The  side  walls  show  the  length  of  the 
pore  (Plate  24,  Fig.  3) ;  while  the  upper  or  lower  wall  shows  the 
outline,  which  is  circular,  and  the  pore,  which  is  very  minute. 

Most  bast  fibres  have  no  cell  contents.  In  some  cases, 
however,  starch  occurs,  as  in  the  bast  fibres  of  rubus. 

The  color  of  the  bast  fibres  varies,  being  colorless,  as  in 
Ceylon  cinnamon;  or  yellowish- white,  as  in  echinacea;  or  bright 
yellow,  as  in  bayberry  bark. 

Bast  fibres  retain  their  living-cell  contents  until  fully  de- 
veloped; then  they  die  and  function  largely  in  a  mechanical 
way. 


104  HISTOLOGY  OF  MEDICINAL  PLANTS 

The  walls  of  bast  fibres  are  composed  of  cellulose  or  of  lignin. 
Most  of  the  bast  fibres  occurring  in  the  medicinal  plants  give 
a  strong  lignin  reaction. 

WOOD   FIBRES 

Wood  fibres  always  occur  in  cross-sections  associated  with 
vessels  and  wood  parenchyma,  from  which  they  are  distin- 
guished by  their  thicker  walls,  smaller  diameter,  and  by  the 
nature  of  the  pores,  which  are  usually  oblique  and  fewer  in 
number  than  the  pores  in  the  walls  of  wood  parenchyma,  and 
different  in  form  from  the  pores  of  vessels. 

The  wood  fibre  on  cross-section  (Plate  105,  Fig.  4)  shows 
an  angled  outline,  except  in  the  case  of  the  fibres  bordering  the 
pith-parenchyma,  etc.,  in  which  case  they  are  rounded  on  their 
outer  surface,  but  angled  at  the  points  in  contact  with  other 
fibres.  The  pore  of  wood  fibres  is  one  of  the  main  characteristics 
which  enable  one  to  distinguish  the  wood  fibres  from  bast  fibres. 

The  pores  are  slanting  or  strongly  oblique  (Plate  28,  Fig.  2), 
and  they  show  for  their  entire  length  on  the  broadest  part  of 
the  wall — i.e.,  the  upper  or  the  lower  surface — while  in  the  side 
wall  they  are  oblique;  but  they  are  not  so  distinct  as  they  are 
on  the  broad  part  of  the  wall. 

Frequently  the  pores  appear  crossed  when  the  upper  and 
the  lower  wall  are  in  focus,  because  the  pores  are  spirally  ar- 
ranged, and  the  pore  on  the  under  wall  throws  a  shadow  across 
the  pore  on  the  upper  wall,  or  vice  versa. 

Wood  fibres  always  occur  in  a  broken  condition  (Plate  28, 
Fig.  i)  in  powdered  drugs.  These  broken  fibres  usually  occur 
both  singly  and  in  groups  in  a  given  powder. 

The  color  of  wood  fibres  varies  greatly  in  the  different  me- 
dicinal woods.  Fragments  of  wood  are  usually  adhering  to 
witch-hazel,  black  haw,  and  other  medicinal  barks.  In  each  of 
these  cases  the  wood  fibres  are  nearly  colorless.  In  barberry 
bark  adhering  fragments  of  wood  and  the  individual  fibres  are 
greenish-yellow.  The  wood  fibres  of  santalum  album  are  whitish- 
brown;  of  quassia,  whitish-yellow;  of  logwood  and  santalum 
rubum,  red. 

Some  wood  fibres  function  as  storage  cells.     In  quassia  the 


PLATE  28 


WOOD  FIBRES 

1.  White  sandal  wood  (Santalum  album,  L.). 

2.  Quassia  wood  (Pier ana  excelsa,  [Swartz]  Lindl.). 

3.  Logwood  with  crystals  (Hamatoxylon  campechianum,  L.)« 

4.  Black  haw  root  (Viburnum  prunifolium,  L.). 


106  HISTOLOGY   OF   MEDICINAL  PLANTS 

wood  fibres  frequently  contain  storage  starch.    The  wood  fibres 
of  logwood  and  red  saunders  contain  coloring  substances,  which 
are  partially  in  the  cell  cavity  and  partially  in  the  cell  wall. 
The  walls  of  wood  are  composed  largely  of  lignin. 

COLLENCHYMA  CELLS 

Collenchyma  cells  form  the  principal  medicinal  tissue  of 
stems  of  herbs,  petioles  of  leaves,  etc.  In  certain  herbs  the 
collenchyma  forms  several  of  the  outer  layers  of  the  cortex  of 
the  stem.  In  motherwort,  horehound,  and  in  catnip  the  col- 
lenchyma cells  occur  chiefly  at  the  angles  of  the  stem.  In 
motherwort  (Plate  29,  Fig.  B)  there  are  twelve  bundles,  one 
large  bundle  at  each  of  the  four  angles,  and  two  small  bundles, 
one  on  either  side  of  the  large  bundle.  In  catnip  (Plate  29, 
Fig.  A)  there  are  four  large  masses,  one  at  each  angle  of 
the  stem. 

Collenchyma  cells  differ  from  parenchyma  cells  in  a  number 
of  ways:  first,  the  cell  cavity  is  smaller;  secondly,  the  walls 
are  thicker,  the  greater  amount  of  thickening  being  at  the  angles 
of  the  cells — that  is,  the  part  of  the  cell  wall  which  is  opposite 
the  usual  intercellular  space  of  parenchyma  cells,  while  the  wall 
common  to  two  adjoining  cells  usually  remains  unthickened. 
In  horehound  stem  (Plate  30,  Fig.  2)  the  thickening  is  so  great 
at  the  angles  that  no  intercellular  space  remains.  In  the  side 
column  of  motherwort  stem  (Plate  30,  Fig.  i)  the  thickening 
between  the  cells  has  taken  place  to  such  an  extent  that  the 
cell  cavities  become  greatly  separated  and  arranged  in  parallel 
concentric  rows. 

The  collenchyma  of  the  outer  angle  of  motherwort  stem 
(Plate  30,  Fig.  3)  is  greatly  thickened  at  the  angles.  There 
are  no  intercellular  spaces  between  the  cells,  and  cell  cavity 
is  usually  angled  in  outline  instead  of  circular,  as  in  the  cells 
of  horehound.  In  certain  plants  intercellular  spaces  occur  be- 
tween the  cells,  and  the  walls  are  striated  instead  of  being  non- 
striated,  as  in  the  stems  of  horehound,  motherwort,  and 
catnip. 

Collenchyma  cells  retain  their  living  contents  at  maturity. 
Many  collenchyma  cells,  particularly  of  the  outer  layers  of 


PLATE   29 


:'£J 


PLATE  30 


COLLENCHYMA   CELLS 

1.  Cross-section  of  a  side  column  of  the  collenchyma  of  motherwort  stem 
(Leonurus  cardiaca,  L.). 

2.  Cross-section   of  the   collenchyma    of    horehound    stem    (Marrubium 
vulgar e,  L.). 

3.  Cross-section  of  the  collenchyma  of  the  outer  angle  of  mother-wort  stem. 


MECHANICAL  TISSUES  109 

bark   and   the   collenchyma   of    the   stems   of   herbs,    contain 
chlorophyll. 

The  walls  of  collenchyma  consist  of  cellulose. 

STONE  CELLS 

Stone  cells,  like  bast  fibres,  are  branched  or  non-branched. 
Each  group  is  then  separated  into  subgroups  according  to  wall 
structure  (whether  striated,  or  pitted  and  striated,  etc.),  thick- 
ness of  wall  and  of  cell  cavity,  color  of  wall  and  of  cell  contents, 
absence  of  color  and  of  cell  contents,  etc. 

BRANCHED    STONE   CELLS 

Branched  stone  cells  occur  in  a  number  of  drugs.  In  witch- 
hazel  bark  (Plate  31,  Fig.  2)  the  walis  are  thick,  white,  and  very 
porous.  In  some  cells  the  branches  are  of  equal  length;  in 
others  they  are  unequal.  In  the  tea-leaf  (Plate  31,  Fig.  i)  the 
walls  are  yellowish  white  and  finely  porous.  When' the  lower 
wall  is  brought  in  focus,  it  shows  numerous  circular  pits.  These 
pits  represent  the  pores  viewed  from  the  end.  The  branches 
frequently  branch  or  fork. 

Branched  stone  cells  also  occur  in  coto  bark,  acer  spicatum, 
staranise,  witch-hazel  leaf,  hemlock,  and  wild-cherry  barks. 

Non-branched  stone  cells  are  divided  into  two  main  groups, 
as  follows: 

1.  Porous  and  striated  stone  cells,  and, 

2.  Porous  and  non-striated  stone  cells. 

POROUS   AND    STRIATED    STONE   CELLS 

Porous  and  striated  walled  stone  cells  occur  in  ruellia  root, 
winter's  bark,  bitter  root,  allspice,  and  aconite.  These  stone 
cells  are  shown  in  Plate  33,  Figs,  i,  2,  3,  4,  and  5. 

The  stone  cells  of  ruellia  root  (Plate  32,  Fig.  i)  are  greatly 
elongated,  rectangular  in  form,  with  thick,  white,  strongly 
porous  walls.  The  central  cavity  is  narrow  and  is  marked  with 
prominent  pores  and  striations. 

The  stone  cells  of  winter's  bark  (Plate  32,  Fig.  2)  vary  from 
elongated  to  nearly  isodiametric.  The  pores  are  very  large, 


PLATE  31 


BRANCHED  STONE  CELLS 

1.  Tea  leaf  (Thea  sinensis,  L.). 

2.  Witch-hazel  bark  (Hamamelis  virginiana,  L.). 

3-  Hemlock  bark  (Tsuga  canadensis,  [L.]  Carr). 

4-  \\'ild-cherry  bark  (Prunus  serotina,  Ehrh.). 


MECHANICAL   TISSUES  111 

the  light  yellowish  wall  is  irregularly  thickened,  and  the  central 
cavity  is  very  large.  The  pores  are  prominent. 

The  stone  cell  of  bitter  root  (Plate  32,  Fig.  3)  is  nearly 
isodiametric.  The  walls  are  yellowish  white  and  strongly  por- 
ous and  striated.  The  central  cavity  is  about  equal  to  the  thick- 
ness of  the  walls. 

The  stone  cell  of  allspice  (Plate  32,  Fig.  4)  is  mostly  rounded 
in  form,  and  when  the  outer  wall  only  is  in  focus  it  shows  numer- 
ous round  and  elongated  pores.  The  central  cavity  is  filled 
with  masses  of  reddish-brown  tannin.  The  stria tions  are  very 
prominent. 

The  diagnostic  stone  cell  of  aconite  (Plate  32,  Fig.  5)  is 
rectangular  or  square  in  outline;  the  walls  are  yellowish  and 
the  central  cavity  has  a  diameter  many  times  the  thickness  of 
the  wall.  The  side  and  surface  view  of  the  pores  is  prominent, 
and  the  striations  are  very  fine. 

POROUS   AND    NON-STRIATED    STONE   CELLS 

Porous  and  non-striated  stone  cells  occur  in  Ceylon  cinna- 
mon, in  calumba  root,  in  dogwood  bark,  in  cubeb,  and  in  echi- 
nacea  root. 

The  diagnostic  stone  cells  of  Ceylon  cinnamon  (Plate  33, 
Fig.  i)  are  nearly  square  in  outline;  the  walls  are  strongly 
porous  and  the  large  central  cavity  frequently  contains 
starch. 

The  stone  cells  of  calumba  root  (Plate  33,  Fig.  2)  vary  in 
shape  from  rectangular  to  nearly  square,  and  the  walls  are 
greenish  yellow,  unequally  thickened,  and  strongly  porous. 
The  typical  stone  cells  contain  several  prisms,  usually  four. 

The  stone  cells  of  dogwood  bark  (Plate  33,  Fig.  3)  have 
thick,  white  walls  with  simple  and  branched  pores.  The  cen- 
tral cavity  frequently  branches 'and  appears  black  when  recently 
mounted,  owing  to  the  presence  of  air. 

The  stone  cells  of  cubeb  (Plate  33,  Fig.  4)  are  very  small, 
mostly  rounded  in  outline,  with  a  great  number  of  very  fine 
simple  pores  which  extend  from  the  outer  wall  to  the  central 
cavity.  The  wall  is  yellow  and  very  thick. 

The  stone  cells  of  echinacea  root  (Plate  33,  Fig.  5)  are  very 
irregular  in  form;  the  walls  are  yellowish  and  porous,  and  the 


112  HISTOLOGY   OF  MEDICINAL  PLANTS 

central  cavity  is  very  large.  A  black  intercellular  substance 
is  usually  adhering  to  portions  of  the  outer  wall. 

The  color  of  the  walls  of  the  different  stone  cells  is  very 
variable.  In  Ceylon  cinnamon  and  ruellia  the  walls  are  color- 
less; in  zanthoxylium,  light  yellow;  in  rumex,  deep  yellow; 
in  cascara  sagrada,  greenish  yellow. 

The  pores  of  stone  cells,  like  the  pores  of  bast  fibres,  are 
either  simple  or  branched,  and  they  may  or  may  not  extend 
through  the  entire  wall.  Many  of  the  shorter  pores  extend  for 
only  a  short  distance  from  the  cell  cavity. 

The  width  of  the  cell  cavity  varies  considerably  in  the  stone 
cells  of  the  different  plants.  In  aconite  (Plate  32,  Fig.  5),  in 
calumba  (Plate  33,  Fig.  2),  and  in  Ceylon  cinnamon  (Plate  33, 
Fig.  i),  the  cell  cavity  is  several  times  greater  than  the  thick- 
ness of  the  cell  wall. 

In  allspice  (Plate  32,  Fig.  4),  in  bitter  root  (Plate  32,  Fig. 
3),  the  diameter  of  the  cell  cavity  and  the  thickness  of  the  wall 
are  about  equal.  In  cubeb  (Plate  33,  Fig.  4),  in  ruellia  (Plate 
32,  Fig.  i),  the  wall  is  thicker  than  the  diameter  of  the  cell 
cavity. 

The  cavity  of  many  stone  cells  contains  no  characteristic 
cell  contents.  In  other  stone  cells  the  ceU  contents  are  as 
characteristic  as  the  stone  cell.  The  stone  cells  of  both  Saigon 
and  Ceylon  cinnamon  (Plate  33,  Fig.  i)  contain  starch;  the 
stone  cells  of  calumba  (Plate  33,  Fig.  2)  contain  prisms  of  calcium 
oxalate;  the  stone  cells  of  allspice  and  sweet-birch  bark  contain 
tannin. 

In  cross-sections,  stone  cells  occur  singly,  as  in  Saigon  cinna- 
mon (Plate  34,  Fig.  i),  ruellia  (Plate  34,  Fig.  2);  in  groups,  as 
in  cascara  sagrada  (Plate  34,  Fig.  3) ;  and  in  continuous  bands, 
as  in  Saigon  cinnamon  (Plate  34,  Fig.  4). 

In  powdered  drugs,  stone  cells,  like  bast  fibres,  occur  singly, 
as  in  ruellia,  calumba,  etc.;  or  in  groups,  as  in  cascara  sagrada, 
witch-hazel  bark,  etc.  In  most  powders  they  occur  both  singly 
and  in  groups. 

The  individual  stone  cells  are  mostly  entire,  as  in  ruellia, 
calumba,  allspice,  echinacea,  etc.  In  cascara  sagrada  many  of 
the  stone  cells  are  broken  when  the  closely  cemented  groups 
are  torn  apart  in  the  milling  process.  Many  of  the  branched 


PLATE  32 


POROUS  AND  STRIATED   STONE   CELLS 

1.  Ruellia  root  (Ruellia  ciliosa,  Pursh.). 

2.  Winter's-bark  (Drimys  winteri,  Forst.). 

3.  Bitterroot  (Apocynum  andros&mifolium,  L.). 

4.  Allspice  (Pimento,  officinalis,  Lindl.). 

5.  Aconite  (Aconitum  napellus,  L.). 


PLATE  33 


POROUS  AND  NON-STRIATED  STONE  CELLS 

1.  Ceylon  cinnamon  (cinnamomum  zeylanicum,  Necs). 

2.  Calumba  root  (Jateorhiza  palmata,  [Lam.]  Micrs). 

3.  Dogwood  root  bark  (Cornus  florida,  L.). 

4.  Cubeb  (Piper  cubeba,  L.,  f.) 

5.  Echinacea  (Echinacea  angustifolia,  D.C.). 


PLATE  34 


1.  Saigon  cinnamon. 

2.  Ruellia  root  (Ruettia  ciliosa,  Pursh.). 

3.  Cascara  sagrada  (Rhamnus  purshiana,  D.C.). 

4.  Saigon  cinnamon. 


116  HISTOLOGY  OF  MEDICINAL  PLANTS 

stone  cells  of  witch-hazel  bark  and  leaf,  wild  cherry,  etc.,  also 
occur  broken  in  the  powder. 

The  walls  of  all  stone  cells  are  composed  of  lignin. 

The  form  of  stone  cells  varies  greatly;  in  aconite  the  stone 
cells  are  quadrangular;  in  ruellia  they  are  rectangular;  in 
pimenta,  circular  or  oval  in  outline;  in  most  stone  cells  they 
are  polygonal. 

The  lignified  walls  of  stone  cells  are  stained  red  with  a 
solution  of  phloroglucin  and  hydrochloric  acid,  and  the  walls 
are  stained  yellow  by  aniline  chloride. 

ENDODERMAL   CELLS 

The  endodermal  cells  of  the  different  plants  vary  greatly 
in  form,  color,  structure,  and  composition  of  the  wall,  yet  these 
different  endodermal  cells  may  be  divided  into  two  groups: 
first,  thin-walled  parenchyma-like  cells,  and,  secondly,  thick- 
walled  fibre-like  cells.  In  the  thin- walled  endodermal  cells  the 
walls  are  composed  of  cellulose,  and  the  cell  terminations  are 
blunt  or  rounded.  When  the  drug  is  powdered  the  cells  break 
up  into  small  diagnostic  fragments.  In  the  thick-walled  endo- 
dermal cells  the  walls  are  lignified  and  porous,  and  the  ends  of 
the  cell  are  frequently  pointed  and  resemble  fibres. 

Sarsaparilla  root,  triticum,  convallaria,  and  aletris  have 
thick- walled  endodermal  cells. 

STRUCTURE   OF   ENDODERMAL   CELLS 

The  endodermal  cells  of  sarsaparilla  root  (Plate  35,  Fig.  i) 
are  never  more  than  one  layer  in  thickness.  The  walls  are 
porous  and  of  a  yellowish-brown  color.  Alternating  with  the 
thick-walled  cell  is  a  thin-walled  cell,  which  is  frequently  re- 
ferred to  as  a  passage  cell. 

The  endodermal  cells  of  triticum  (Plate  35,  Fig.  2)  are  yellow- 
ish and  the  walls  are  porous  and  striated.  There  are  one  or  two 
layers  of  cells.  The  cells  forming  the  outer  layer  have  very 
thin  outer  but  thick  inner  walls,  while  the  cells  forming  the 
inner  layer  are  more  uniform  in  thickness. 

The  endodermal  cells  of  convallaria  (Plate  35,  Fig.  3)  are 
yellowish  white  in  color,  and  the  walls  are  porous  and  striated. 


PLATE  35 


CROSS-SECTIONS  OF  ENDODERMAL  CELLS  OF 

1.  Sarsaparilla  root  (Smilax  officinalis,  Kunth) 

2.  Triticum  (Agropyron  repens,  L.). 

3.  Convallaria  (Convallaria  majalis,  L.) 

4.  Aletris  (Aletris  farinosa,  L.). 


118  HISTOLOGY   OF   MEDICINAL   PLANTS 

The  outer  wall  of  the  layer  of  cells  is  thinner  than  the  inner 
wall.     The  innermost  layer  of  cell  is  more  uniformly  thickened. 

The  endodermal  cells  of  aletris  (Plate  35,  Fig.  4)  are  yellow- 
ish brown,  slightly  porous  and  striated.  There  are  one  or  two 
layers  of  these  cells,  and  two  of  the  smaller  cells  usually  occupy 
a  space  similar  to  that  occupied  by  the  radically  elongated 
single  cell. 

On  longitudinal  view  the  endodermal  cells  of  sarsaparilla 
triticum,  convallaria,  and  aletris  appear  as  follows: 

Those  of  sarsaparilla  (Plate  36,  Fig.  i)  are  greatly  elongated, 
the  ends  of  the  cells  are  blunt  or  slightly  pointed,  and  the  walls 
appear  porous  and  striated. 

Those  of  triticum  (Plate  36,  Fig.  2)  are  elongated,  the  walls 
are  porous  and  striated,  and  the  outer  wall  is  much  thinner 
than  the  inner  wall.  The  end  wall  between  two  cells  frequently 
appears  common  to  the  two  cells. 

Those  of  convallaria  (Plate  36,  Fig.  3)  are  elongated,  and 
the  end  wall  is  usually  blunt.  The  outer  wall  is  thinner  than 
the  inner  wall. 

Those  of  aletris  (Plate  36,  Fig.  4)  are  fibre-like  in  appear- 
ance; the  ends  of  the  cells  are  pointed  and  the  wall  is  strongly 
porous.  The  longitudinal  view  of  these  cells  is  shown  in  plate  36. 

HYPODERMAL   CELLS 

Hypodermal  cells  occur  in  sarsaparilla  root  and  in  triticum. 
In  the  cross-section  of  sarsaparilla  root  (Plate  37,  Fig.  i)  the 
hypodermal  cells  are  yellowish  or  yellowish  brown.  The  outer 
wall  is  thicker  than  the  inner  wall,  the  cell  cavity  is  mostly 
rounded,  and  contains  air.  The  walls  are  porous  and  finely 
striated.  On  longitudinal  view  the  hypodermal  cells  of  sarsa- 
parilla (Plate  37,  Fig.  2)  are  greatly  elongated;  the  outer  and 
side  walls  are  thicker  than  the  inner  walls.  The  ends  of  the 
cells  are  blunt  and  distinct  from  each  other. 

In  cross- section  the  hypodermal  cells  of  triticum  (Plate  37* 
Fig.  3)  are  nearly  rounded  in  outline,  and  the  walls  are  of  nearly 
uniform  thickness.  In  longitudinal  view  (Plate  37,  Fig.  4) 
the  same  cells  appear  parenchyma-like,  and  the  walls  between 
any  two  cells  appear  common  to  the  two  cells. 


PLATE   36 


LONGITUDINAL  SECTIONS  OF  ENDODERMAL  CELLS 

1.  Sarsaparilla  root  (Smilax  officinalis,  Kunth). 

2.  Triticum  (Agropyron  repens,  L.). 

3.  Convallaria  (Convallaria  majalis,  L.). 

4.  Aletris  (Aletris  farinosa,  L.). 


PLATE  37 


HYPODERMAL  CELLS 

1.  Cross-section  sarsaparilla  root  (Smile x  officinalis,  Kunth). 

2.  Longitudinal  section  sarsaparilla  root  (Smilax  officinalis,  Kunth). 

3.  Cross-section  triticum  (Agropyron  repens,  L.). 

4.  Longitudinal  section  triticum  (Agropyron  repens,  L.). 


CHAPTER  IV 

ABSORPTION   TISSUE 

Most  plants  obtain  the  greater  part  of  their  food,  first,  from 
the  soil  in  the  form  of  a  watery  solution,  and,  secondly,  from  the 
air  in  the  form  of  a  diffusible  gas.  In  a  few  cases  all  the  food 
material  is  obtained  from  the  air,  as  in  the  case  of  epiphytic 
plants.  In  such  plants  the  aerial  roots  have  a  modified  outer 
layer — velamen — which  functions  as  a  water-absorbing  and  gas- 
condensing  tissue.  Many  xerophytic.  plants  absorb  water 
through  the  trichomes  of  the  leaf.  Such  absorption  tissue 
enables  the  plant  to  absorb  any  moisture  that  may  condense 
upon  the  leaf  and  that  would  not  otherwise  be  available  to  the 
plant.  The  water-absorbing  tissue  of  roots  is  restricted  to  the 
root  hairs,  which  are  found,  with  few  exceptions,  only  on  young 
developing  roots. 

ROOT  HAIRS 

Root  hairs  usually  occur  a  short  distance  back  of  the  root 
cap.  There  is,  in  fact,  a  definite  zone  of  the  epidermis  on  which 
the  root  hairs  develop.  This  zone  is  progressive.  As  the  root 
elongates  the  root  hairs  continue  to  develop,  the  zone  of  hairs 
always  remaining  at  about  the  same  distance  from  the  root 
cap.  With  the  development  of  new  zones  of  growth  the  hairs 
on  the  older  zone  die  off  and  finally  become  replaced  by  an  epi- 
dermis, or  a  periderm,  except  in  the  case  of  sarsaparilla  root,  and 
possibly  other  roots  that  have  persistent  root  hairs. 

Each  root  hair  is  an  outgrowth  from  an  epidermal  cell  (Plate 
38,  Fig.  3).  The  length  of  the  hair  and  its  form  depend  upon 
the  nature  of  the  soil,  whether  loose  or  compact,  and  upon  the 
amount  of  water  present. 

A  root  hair  is  formed  by  the  extension  of  the  peripheral  wall 
of  an  epidermal  cell.  At  first  this  wall  is  only  slightly  papillate, 
but  gradually  the  end  wall  is  extended  farther  and  farther  from 

121 


122  HISTOLOGY    OF   MEDICINAL   PLANTS 

the  surface  of  the  root,  caused  by  the  development  of  side 
walls  by  the  growing  tip  of  the  root  hair  until  a  tube-like  struc- 
ture, root  hair,  is  produced.  The  root  hair  is  then  a  modified 
epidermal  cell.  The  protoplast  lines  the  cell,  and  the  central 
part  of  the  root  hair  consists  of  a  large  vacuole  filled  with  cell 
sap.  The  wall  of  the  root  hair  is  composed  of  cellulose,  and 
the  outermost  part  is  frequently  mucilaginous.  As  the  root 
hairs  develop,  they  become  bent,  twisted,  and  of  unequal  diam- 
eter, as  a  result  of  growing  through  narrow,  winding  soil 
passages.  During  their  growth,  the  root  hairs  become  firmly 
attached  to  the  soil  particles.  The  walls  of  root  hairs  give  an 
acid  reaction  caused  by  the  solution  of  the  carbon  dioxide  ex- 
creted by  the  root  hair.  The  acid  character  of  the  wall  attracts 
moisture,  and  in  addition  has  a  solvent  action  on  the  insoluble 
compounds  contained  in  the  soil.  It  will  thus  be  seen  that  the 
method  of  growth,  structure,  composition,  and  reaction  of  the 
wall  of  the  root  hair  is  perfectly  suited  to  carry  on  the  work 
of  absorbing  the  enormous  quantities  of  water  needed  by  the 
growing  plant.  It  is  a  well-known  fact  that  when  two  solutions 
of  unequal  density  are  separated  by  a  permeable  membrane, 
the  less  dense  liquid  will  pass  through  the  membrane  to  the 
denser  liquid.  The  wall  of  the  root  hair  acts  like  an  osmatic 
membrane.  The  less  dense  watery  solution  outside  the  root 
hair  passes  through  its  wall  and  into  the  denser  cell  sap  solution. 
As  the  solution  is  absorbed,  it  passes  from  the  root  hair  into 
the  adjoining  cortical  parenchyma  cells. 

It  is  a  fact  that  root  hairs  are  seldom  found  in  abundance 
on  medicinal  roots.  This  is  due  to  the  fact  that  root  hairs 
occur  only  on  the  smaller  branches  of  the  root,  and  that  when 
the  root  is  pulled  from  the  ground  the  smaller  roots  with  their 
root  hairs  are  broken  off  and  left  in  the  soil.  For  this  reason 
a  knowledge  of  the  structure  of  root  hairs  is  of  minor  importance 
in  the  study  of  powdered  drugs.  An  occasional  root  hair  is 
found,  however,  in  most  powdered  roots,  but  root  hairs  have 
little  or  no  diagnostic  value,  except  in  false  unicorn  root  and 
sarsaparilla.  When  false  unicorn  root  is  collected,  most  of  the 
root  hairs  remain  attached  to  the  numerous  small  fibrous  roots, 
owing  to  the  fact  that  these  roots  are  easily  removed  from  the 
sandy  soil  in  which  the  plants  grow.  The  root  hairs  of  false 


CROSS-SECTION  OF  SARSAPARILLA  ROOT  (Smilax  ojjicinalis,  Kunth) 

1 .  Epidermal  cell  developing  into  a  root  hair. 

2.  Developing  root  hair. 

3.  Nearly  mature  root  hair. 

4.  Hypodermal  cells. 


PLATE  39 


ROOT  HAIRS  (Fragments) 

1.  Sarsaparilla  root  (Smilax  officinalis,  Kunth), 

2.  False  unicorn  root  (Helonias  bullata,  L.). 


ABSORPTION  TISSUE  125 

unicorn  are  so  abundant  and  so  large  that  they  form  dense 
mats,  which  are  readily  seen  without  magnification.  These 
hairs  are,  therefore,  macroscopically  as  well  as  microscopically 
diagnostic.  The  root  hairs  of  false  unicorn  (Plate  39,  Fig.  2) 
have  white,  wavy,  often  decidedly  indented  walls.  The  terminal, 
or  end  wall,  is  rounded  and  much  thicker  than  the  side  walls. 
In  sarsaparilla  (Plate  39,  Fig.  i)  the  root  hairs  are  curved 
and  twisted.  The  end  wall  is  thicker  than  the  side  walls.  In 
some  hairs  the  walls  are  as  thick  as  the  walls  of  the  thin-walled 
bast  fibres.  This  accounts  for  the  fact  that  the  root  hairs 
are  persistent  on  even  the  older  portions  of  sarsaparilla  root, 
and  it  serves  also  to  explain  why  these  root  hairs  remain  on 
the  root  even  after  being  pulled  from  the  firmly  packed  earth 
in  which  the  root  grows. 

WATER  ABSORPTION  BY   LEAVES 

In  many  xerophytic  terrestrial  plants,  the  trichomes  occurring 
on  leaves  act  as  a  water-absorbing  tissue.  In  such  plants  the 
walls  of  the  hairs  are  composed  largely  of  cellulose.  It  is  ob- 
vious that  these  hairs  absorb  the  water  of  condensation  caused 
by  dew  and  light  rains — water,  which  could  not  reach  the  plant 
except  by  such  means. 

There  is  no  special  tissue  set  aside  for  the  absorption  of 
gases  from  the  air.  Carbon  dioxide,  which  contributes  the 
element  carbon  to  the  starch  formed  by  photosynthesis,  enters 
the  leaf  by  way  of  the  stoma  and  lenticels.  The  structure  and 
the  chief  functions  of  these  will  be  considered  under  aerating 
tissue. 


CHAPTER  V 

CONDUCTING   TISSUE 

All  cells  of  which  the  primary  or  secondary  function  is  that 
of  conduction  are  included  under  conducting  tissue.  It  will 
be  understood  how  important  the  conducting  tissue  is  when  the 
enormous  quantity  of  water  absorbed  by  a  plant  during  a 
growing  season  is  considered.  It  will  then  be  realized  that 
the  conducting  system  must  be  highly  developed  in  order  to 
transport  this  water  from  one  organ  to  another,  and,  in  fact, 
to  all  the  cells  of  the  plant.  Special  attention  must  be  given  to 
the  occurrence,  the  structure,  the  direction  of  conduction,  and 
to  the  nature  of  the  conducted  material. 

The  cells  or  ^cell  groups  comprising  the  conducting  tissue 
are  vessels  and  tracheids,  sieve  tubes,  medullary  ray  cells,  latex 
tubes,  and  parenchyma. 

VESSELS 

Vessels  and  tracheids  form  the  principal  upward  con- 
ducting tissue  of  plants.  They  receive  the  soil  water  expressed 
from  the  cortical  parenchyma  cells  located  in  the  region  of  the 
root,  immediately  back  of  the  root  hair  zone.  This  soil  water, 
with  dissolved  crude  inorganic  and  organic  food  materials,  after 
entering  the  vessels  and  tracheids  passes  up  the  stem.  The 
cells  needing  water  at  the  different  heights  absorb  it  from  the 
vessels,  the  excess  finally  reaching  the  leaves.  When  the  stem 
branches,  the  water  passes  into  the  vessels  of  the  branches  and 
finally  to  the  leaves  of  the  branch.  In  certain  special  cases  the 
vessels  conduct  upward  soluble  food  material.  In  spring  sugary 
sap  flows  upward  through  the  vessels  of  the  sugar  maple. 

Vessels  are  tubes,  often  of  great  length,  formed  from  a  number 
of  superimposed  cells,  in  which  the  end  walls  have  become 
absorbed.  The  vessels  therefore  offer  little  resistance  to  the 
transference  of  water  from  the  roots  to  the  leaves  of  a  plant. 

126 


CONDUCTING  TISSUE  127 

The  combined  length  of  the  vessels  is  about  equal  to  the  height 
of  the  plant  in  which  they  occur.  The  length  of  the  individual 
vessels  varies  from  a  fraction  of  a  meter  up  to  several  meters. 

ANNULAR  VESSELS 

The  annular  vessels  are  thickened  at  intervals  in  the  form 
of  rings  (Plate  40,  Fig.  i),  which  extend  outward  from  and 
around  the  inner  wall  of  the  vessel.  In  fact,  it  is  the  inner  wall 
which  is  thickened  in  all  the  different  types  of  vessels.  The 
ring-like  thickening  usually  separates  from  the  wall  when  the 
drug  is  powdered.  Such  separated  rings  occur  frequently  in 
powdered  digitalis,  belladonna,  and  stramonium  leaves.  An- 
nular vessels  are  not,  however,  of  diagnostic  importance,  be- 
cause more  characteristic  cells  are  found  in  the  plants  in  which 
they  occur.  Not  infrequently  a  vessel  will  have  annular  thick- 
enings at  one  end  and  spiral  thickenings  at  the  other.  Such 
vessels  are  found  in  the  pumpkin  stem  (Plate  40,  Fig.  i). 

Vessels  are  distinguished  from  other  cells  by  their  arrange- 
ment, by  their  large  size  when  seen  in  cross-section,  and  by  the 
thickening  of  the  wall  when  seen  in  longitudinal  sections  of  the 
plant  or  in  powders.  The  side  walls  of  vessels  are  thickened  in 
a  number  of  striking  yet  uniform  ways.  The  chief  types  of 
thickening  of  the  wall,  beginning  with  one  that  is  the  least 
thickened,  are  annular,  spiral,  sclariform,  pitted,  and  pitted 
with  bordered  pores. 

SPIRAL  VESSELS 

In  the  spiral  vessel  the  thickening  occurs  in  the  form  of  a 
spiral,  which  is  readily  separated  from  the  side  walls.  This  is 
particularly  the  case  in  powdered  drugs,  where  the  spiral  thick- 
ening so  frequently  separates  from  the  cell  wall.  There  are 
three  types  of  spiral  vessels:  those  with  one  (Plate  41,  Fig.  i), 
those  with  two,  and  those  with  three  spirals.  Single  spirals 
occur  in  most  leaves;  double  spirals  occur  in  many  plants 
(Plate  41,  Fig.  2),  but  they  are  particularly  striking  in  pow- 
dered squills.  Triple  spirals  are  characteristic  of  the  eucalyptus 
leaf  (Plate  41,  Fig.  3);  in  fact,  they  form  a  diagnostic  feature 
of  the  powder.  Frequently  a  spirally  thickened  wall  indicates 
a  developmental  stage  of  the  vessel.  Many  such  vessels  are 


128  HISTOLOGY   OF   MEDICINAL  PLANTS 

spirally  thickened  at  first,  but  later,  when  mature,  an  increased 
amount  of  thickening  occurs  and  the  vessel  becomes  a  reticulate 
or  pitted  vessel.  Many  mature  vessels,  however,  are  spirally 
thickened  as  indicated  above.  In  herbaceous  stems  and  in 
certain  roots  and  leaves  spiral  vessels  are  associated  with  the 
sclariform  reticulate  "and  pitted  type.  In  certain  cases  a  single 
spiral  band  will  branch  as  the  vessel  matures. 

There  is  a  great  variation  in  the  amount  of  spiral  thickening 
occurring  in  a  vessel.  In  leaves,  particularly,  the  spiral  appears 
loosely  coiled;  while  in  squills  and  other  rhizomes  and  roots 
the  spiral  appears  as  a  series  of  rings.  When  viewed  by  high 
power  only  half  of  each  spiral  band  is  visible.  At  either  side 
of  the  cell  the  exact  size  and  form  of  the  thickening  appear  in 
two  parallel  rows  of  dark  circles  or  projections  from  the  walls. 
This  thickening  of  the  wall  is  rendered  visible  from  the  fact 
that  the  light  is  retarded  as  it  passes  through  that  portion  of  the 
spiral  extending  from  the  upper  to  the  under  side  of  the  spiral; 
while  the  light  readily  traverses  the  upper  and  lower  cross  bands 
of  the  vessel. 

It  should  be  remembered  that,  when  the  upper  part  of  the 
spiral  vessel  is  in  focus,  the  bands  appear  to  bend  in  a  direction 
away  from  the  eye;  while  when  the  under  side  of  the  bands  are 
in  focus,  the  bands  appear  to  bend  toward  the  eye.  These 
facts  will  show  that  it  is  necessary  to  focus  on  both  the  upper 
and  lower  walls  in  studying  spiral  vessels.  In  double  spiral 
vessels  the  spirals  are  frequently  coiled  in  opposite  directions; 
therefore  the  bands  appear  to  cross  one  another.  In  eucalyptus 
leaf  the  three  bands  are  coiled  in  the  same  direction.  In  all 
cases  the  thickening  occurs  on  all  sides  of  the  wall.  Its  appear- 
ance will,  therefore,  be  the  same  no  matter  at  what  angle  the 
vessel  is  viewed. 

SCLARIFORM  VESSELS 

Sclariform  vessels  have  interrupted  bands  of  thickening  on 
the  inner  walls.  Two  or  more  such  bands  occur  between  the 
two  side  walls.  The  series  of  bands  are  separated  by  uniformly 
thickened  portions  of  the  wall  extending  parallel  to  the  length 
of  the  vessel.  Sclariform  vessels  are  usually  quite  broad,  so 
that  it  is  necessary  to  change  the  focus  several  times  in  order 


PLATE  40 


ANNULAR  AND  SPIRAL  VESSELS 

1.  Pumpkin  stem  (Cucurbita  pepo,  L.). 

2.  Two  characteristic  views  of  spiral  vessels. 

3.  (A)  Upper  part  of  spiral  vessel  in  focus. 
(B)  Under  part  of  spiral  vessel  in  focus. 

4.  Spiral  vessel  of  the  disk  petal  matricaria  (Matricaria 
chamoniilla,  L.). 


PLATE  41 


SPIRAL  VESSELS 

1.  Single  spiral  vessel  of  pumpkin  stem  (Cucurbita  pepo,  L.). 

2.  Double  spiral  vessel  of  squill  bulb  (Urginea  maritima,  [L.J  Baker). 

3.  Triple  spiral  vessel  of  eucalyptus  leaf  (Eucalyptus  globulus,  Labill). 


CONDUCTING  TISSUE  131 

to  bring  the  different  series  of  bands  in  focus.    The  series  of 
bands  are  usually  of  unequal  width  and  length. 

Sclariform  vessels  occur  in  male  fern  (Plate  42,  Fig.  2), 
calamus,  tonga  root  (Plate  42,  Fig.  3),  and  sarsaparilla  (Plate 

42,  Fig.  i).     In  each  they  are  characteristic.     Sclariform  vessels, 
with  these  few  exceptions,  do  not  occur  in  drug  plants.     In  fact, 
drugs  derived  from  dicbtyledones  rarely  have  sclariform  vessels. 
They  occur  chiefly  in  the  ferns  and  drugs  derived  from  mono- 
cotyledenous  plants.     Their  presence  or  absence  should,  there- 
fore, be  noted  when  studying  powdered  drugs. 

,    RETICULATE  VESSELS 

Reticulate  vessels  are  of  common  occurrence  in  medicinal 
plants.  In  fact,  they  occur  more  frequently  than  any  other 
type  of  vessel.  The  basic  structure  of  reticulate  vessels  (Plate 

43,  Fig.  i)  occurring  in  different  plants  is  similar,  but  they  vary 
in  a  recognizable  way  in  different  plants   (Plate  43,  Fig.   2). 
The  walls  of  reticulate  vessels  are  thickened  to  a  greater  extent 
than  are  the  walls  of  spirally  thickened  vessels. 

PITTED  VESSELS 

Pitted  vessels  are  met  with  most  frequently  in  woods  and 
wood-stemmed  herbs.  There  are  two  distinct  types  of  pitted 
vessels — i.e.,  simple  pitted  vessels  and  pitted  vessels  with 
bordered  pores. 

The  pitted  vessel  represents  the  highest  type  of  cell-wall 
thickening.  The  entire  wall  of  the  vessel  is  thickened,  with 
the  exception  of  the  places  where  the  pits  occur.  The  number 
and  size  of  the  pits  vary  greatly  in  different  drugs.  In  quassia 
(Plate  44,  Fig.  i)  the  pits  are  numerous  and  very  small,  and  the 
openings  are  nearly  circular  in  outline.  In  white  sandalwood 
(Plate  44,  Fig.  3).  the  pits  are  few  in  number,  but  when  they 
do  occur  they  are  much  larger  than  are  the  pits  of  quassia. 

PITTED  VESSELS  WITH  BORDERED  PORES 

Pitted  vessels  with  bordered  pores  are  of  common  occur- 
rence in  the  woody  stems  and  stems  of  many  herbaceous  plants 
(Plate  45,  Figs.  3  and  4).  In  such  vessels  the  wall  is  un thickened 
for  a  short  distance  around  the  pits.  This  unthickened  portion 


PLATE  42 


SCLARIFORM    VESSELS 

1.  Sarsaparilla  root  (Smilax  officinalis,  Kunth). 

2.  Male  fern  (Dryopteris  marginalis,  [L.]  A.  Gray), 

3.  Tonga  root. 


PLATE  43 


RETICULATE  VESSELS 

1.  Hydrastis  rhizome  (Hydrastis  canadensis,  L.). 

2.  Musk  root  (Ferula  sumbul,  [Kauffm.j  Hook.,  f.). 


PLATE  44 


PITTED  VESSELS 

1.  Quassia,  low  magnification  (Picrcena  excelsa,  [Swartz]  Lincll.). 

2.  Quassia,  high  magnification. 

3.  White  sandal  wood  (Santalum  album,  L.). 


PLATE  45 


VESSELS 

1.  Reticulate  vessel  of  calumba  root  (Jateorhiza  palmata,  [Lam.]  Miers). 

2.  Reticulate  tracheid  of  hydrastis  rhizome  (Hydrastis  canadensis,  L.). 

3.  Pitted  vessel  with  bordered  pores  of  belladonna  stem. 

4.  Pitted  vessel  with  bordered  pores  of  aconite  stem  (Aconitum  napellus ,L.) . 


136  HISTOLOGY    OF   MEDICINAL  PLANTS 

may  be  either  circular  or  angled  in  outline,  a  given  form  being 
constant  to  the  plant  in  which  it  occurs.  The  pits  vary  from 
oval  to  circular.  Pitted  vessels  with  bordered  pores  occur  in 
belladonna  and  aconite  stems. 

Vessels  and  tracheids  lose  their  living-cell  contents  when 
fully  developed.  In  the  vessels  the  cell  contents  disappear  at 
the  period  of  dissolution  of  the  cell  wall. 

The  walls  of  vessels  and  tracheids  are  composed  of  lignin, 
a  substance  which  prevents  the  collapsing  of  the  walls  when 
the  surrounding  cells  press  upon  them,  and  which  also  prevents 
the  tearing  apart  of  the  wall  when  the  vessel  is  filled  with  ascend- 
ing liquids  under  great  pressure.  Lignin  thus  enables  the 
vessel  to  resist  successively  compression  and  tearing  forces. 

Tracheids  are  formed  from  superimposed  cells  with  oblique 
perforated  end  walls.  The  side  walls  of  tracheids  are  thickened 
in  a  manner  similar  to  those  of  vessels.  The  tracheids  in  golden 
seal  are  of  a  bright-yellow  color,  and  groups  of  these  short 
tracheids  scattered  throughout  the  field  form  the  most  char- 
acteristic part  of  the  powdered  drug.  In  ipecac  root  the  tracheids 
are  of  a  porcelain-white,  translucent  appearance,  and  they  are 
much  longer  than  are  the  tracheids  of  golden  seal. 

The  cellulose  walls  of  parenchyma  cells  are  stained  blue 
with  haematoxylin  and  by  chlorzinciodide.  Cellulose  is  com- 
pletely soluble  in  a  fresh  copper  ammonia  solution. 

SIEVE   TUBES 

Sieve  tubes  are  downward-conducting  cells.  They  conduct 
downward  proteid  food  material.  This  fact  is  easily  demon- 
strated by  adding  iodine  to  a  section  containing  sieve  tubes,  in 
which  case  the  sieve  tubes  are  turned  yellow. 

Developing  sieve  tubes  have  all  the  parts  common  to  a  living 
cell;  but  when  fully  mature,  however,  the  nucleus  becomes 
disorganized,  but  a  layer  of  protoplasm  continues  to  line  the 
cell  wall. 

Sieve  tubes  (Plate  46,  Fig.  i)  are  composed  of  a  great  number 
of  superimposed  cells  with  perforated  end  walls  and  with  non- 
porous  cellulose  side  walls.  The  end  walls  of  two  adjoining 
cells  are  greatly  thickened  and  the  pores  pass  through  both 


PLATE  46 


1.  Longitudinal  section  of  sieve  tube  (Cucurbita  pepo,  L.). 

2.  Cross-section  of  sieve  tube  just  above  an  end  wall — sieve  plate. 


138  HISTOLOGY   OF   MEDICINAL  PLANTS 

walls.  This  thickened  part  of  the  porous  end  walls  of  two  sieve 
cells  is  called  the  sieve  plate,  and  it  may  be  placed  in  an  oblique 
or  a  horizontal  position. 

In  a  longitudinal  section  the  sieve  tubes  are  seen  to  be 
slightly  bulging  at  the  sieve  plate,  and  through  the  pores  extend 
protoplasmic  strands.  The  strands  are  united  on  the  upper 
and  lower  side  of  the  sieve  plate  to  form  the  protoplasmic  strands 
of  the  living  sieve  tubes  and  the  callus,  layers  of  dried  plants. 
This  callus  is  frequently  yellowish  in  color,  and  in  all  cases  is 
separated  from  the  cell  wall.  In  certain  plants  the  sieve  plate 
occurs  on  the  side  walls  of  the  sieve  tubes  in  contact  with  other 
sieve  tubes. 

SIEVE  PLATE 

Sieve  plates  on  cross-section  (Plate  46,  Fig.  2)  are  polygonal 
in  outline,  and  the  pores  are  either  round  or  angled.  Large 
sieve  tubes  and  sieve  plates  occur  in  pumpkin  stem;  but,  almost 
without  exception,  in  drug  plants  the  sieve  tubes  are  small 
and  the  sieve  plate  is  inconspicuous.  When  the  drug  is  pow- 
dered, the  sieve  tubes  break  up  into  undiagnostic  fragments. 
When  studying  sections  of  the  plants,  the  extent,  size,  and 
arrangement  of  the  sieve  tubes  must  always  be  noted. 

MEDULLARY  BUNDLES,   RAYS,   AND   CELLS 
Function 

The  medullary  ray  cells  are  the  lateral  conducting  cells  of 
the  plant.  They  conduct  outwardly  the  water  and  inorganic 
salts  brought  up  from  the  roots  by  the  vessels  and  tracheids; 
and  they  conduct  inwardly  toward  the  centre  of  the  stem  the 
food  material  manufactured  in  the  leaves  and  brought  down  by 
the  sieve  cells.  The  medullary  rays  thus  distribute  the  in-, 
organic  and  organic  food  to  the  living  cells  of  the  plant,  and 
they  conduct  the  reserve  food  material  to  the  storage  cells,  and, 
lastly,  they  function  in  certain  plants  as  storage  cells. 

Occurrence 

The  form,  size,  wall  structure,  and  the  distribution  of  the 
medullary  ray  bundles,  rays,  and  cells  are  best  ascertained  by 


CONDUCTING  TISSUE  139 

studying:     first,  the  cross-section  of  the  plant;    secondly,  the 
radial  section;  and,  thirdly,  the  tangential  section. 

Students  should  be  careful  to  distinguish  between  the  medul- 
lary ray  bundle,  the  medullary  ray,  and  the  medullary  ray  cell. 
In  some  plants  the  bundles  are  only  one  cell  wide,  but  in  other 
plants  the  medullary  ray  bundle  is  more  than  one  cell  wide, 
frequently  several  cells  wide. 

THE  MEDULLARY  RAY  BUNDLE 

The  medullary  ray  bundle  is  made  up  of  a  great  many  medul- 
lary ray  cells.  These  bundles  (Plate  106,  Fig.  5)  are  of  variable 
length,  height,  and  width.  The  bundles  are  isolated,  and  they 
occur  among  and  separate  the  other  cells  of  the  plants  in  which 
they  occur.  Tangential  sections  show  the  medullary  ray 
bundle  in  cross-section.  Such  sections  are  lens-shaped,  and 
they  show  both  the  width  and  the  height  of  the  medullary  ray 
bundle.  The  length  of  the  meduQar"  ray  bundle  is  shown  in 
cross-sections. 

THE  MEDULLARY  RAY 

The  medullary  ray  (Plate  47)  is  a  term  used  to  indicate 
that  part  of  a  medullary  ray  bundle  which  is  seen  in  cross- 
sections  and  in  radial  sections.  In  cross-sections  the  length 
of  the  ray  will  be  as  great  as  the  length  of  the  bundle,  and  the 
width  of  the  ray  will  be  as  great  as  the  width  of  the  medullary 
ray  bundle  at  the  point  cut  across.  In  longitudinal  sections  the 
medullary  ray  will  differ  in  height  according  to  the  thickness  of 
the  bundle  at  the  point  cut. 

When  the  medullary  rays  extend  from  the  centre  of  the  stem 
to  the  middle  bark,  they  are  termed  primary  medullary  rays; 
when  they  extend  from  the  cambium  circle  to  the  middle  bark, 
they  are  termed  secondary  medullary  rays.  As  the  plant  grows, 
the  diameter  of  the  organ  becomes  greater  and  the  number  of 
medullary  rays  are  increased.  In  each  of  these  cases  the  medul- 
lary rays  may  be  one  or  more  than  one  cell  wide,  according  to 
whether  the  medullary  ray  bundle  is  one  or  more  than  one  cell 
wide.  Even  in  the  same  plant  the  width  of  the  medullary  rays 
will  vary  if  the  bundle  is  more  than  one  cell  wide,  according  to 
width  of  the  medullary  ray  bundle  at  the  point  cut  across. 


PLATE  47 


RADIAL  LONGITUDINAL  SECTION  OF  WHITE  SANDAL  WOOD  (Santalum  album,  L.) 

1 .  Medullary  ray. 

2.  Wood  fibres  and  wood  parenchyma. 


CONDUCTING   TISSUE  141 

On  cross-section  the  medullary  rays  are  seen  to  vary  greatly. 
In  many  plants  they  are  more  or  less  straight  radial  lines,  as 
in  quassia  (Plate  105,  Fig.  2);  while  in  other  plants  they  form 
wavy  lines  where  they  bend  or  curve  around  the  conducting 
cells,  as  in  piper  methysticum,  kava-kava  (Plate  48,  Fig.  A). 

In  the  study  of  powdered  drugs  the  radial  view  of  the  medul- 
lary rays  is  most  frequently  seen. 

In  a  perfect  radial  section  (Plate  107,  Fig.  2)  the  medullary 
rays  are  seen  as  tiers  of  cells  in  contact  throughout  their  long 
diameter,  and  they  run  at  right  angles  to  the  long  diameter  of 
the  other  cells.  This  view  of  the  rays  shows  the  length  and 
height  of  the  medullary  ray.  In  logwood  the  rays  are  often 
forty  cells  high.  In  powdered  barks,  woods  (Plate  47),  and 
woody  roots  the  radial  view  of  the  medullary  rays  is  frequently 
diagnostic. 

In  guaiacum  officianale  wood  the  medullary  rays  are  one 
cell  wide  on  cross-section,  and  up  to  six  cells  high  on  the  tan- 
gential section.  In  santalum  album  the  rays  are  from  one  to 
three  cells  wide  on  cross-section,  and  up  to  six  cells  high  on 
tangential  section.  In  the  greater  number  of  plants  the  rays 
are  more  than  one  cell  wide. 

THE  MEDULLARY  RAY  CELL 

The  medullary  ray  cell  (Plate  48,  Fig.  i)  is  one  of  the  in- 
dividual cells  making  up  the  medullary  ray  bundle  and  the 
medullary  ray. 

The  cross-sections  of  the  cells  which  are  seen  in  tangential 
sections  show  the  cells  to  be  mostly  circular  in  outline  when 
they  occur  in  the  central  portion  of  medullary  ray  bundles  of 
more  than  two  cells  in  width;  but  they  are  more  irregular  in 
outline  when  the  medullary  ray  bundle  is  only  one  cell  wide. 
Even  the  cells  of  the  three  or  more  cell-wide  bundles  have  ir- 
regular, outlined  cells  at  the  ends  of  the  bundle  and  on  the  sides 
in  contact  with  the  other  tissues. 

The  length  and  height  of  the  medullary  ray  cell  are  shown 
in  radial  sections;  while  the  width  and  length  of  the  medullary 
ray  cells  are  shown  in  cross-sections. 


142  HISTOLOGY   OF   MEDICINAL   PLANTS 

Structure  of  Cells 

The  structure  of  the  individual  cells  forming  the  medullary 
rays  differs  greatly  in  different  plants,  but  is  more  or  less  con- 
stant in  structure  in  a  given  species. 

The  medullary  rays  of  the  wood  usually  have  strongly  pitted 
side  and  end  walls,  while  the  medullary  rays  of  most  barks  are 
not  at  all,  or  only  slightly,  pitted.  In  most  plants  the  cells  are 
of  nearly  uniform  size.  Frequently,  however,  the  cells  vary  in 
size  in  a  given  ray,  as  shown  in  the  cross-section  of  kava-kava. 

Arrangement  of  the  Cells  in  a  Ray 

The  union  of  any  two  cells  in  a  ray  is  also  of  importance. 
In  quassia  the  medullary  ray  cells  have  oblique  end  walls,  so 
that  on  cross-section  the  line  of  union  between  two  cells  is  an 
oblique  wall.  In  most  plants  the  medullary  ray  cells  have 
blunt  or  square  or  oblique  end  walls,  so  that  the  line  of  union 
is  a  straight  line. 

In  most  plants  the  cells  are  much  longer  than  broad,  but  the 
cells  of  sassafras  bark  are  nearly  as  broad  as  long. 

The  walls  of  the  cortical  medullary  ray  cells  and  the  medul- 
lary rays  of  most  roots  and  stems  of  herbs  are  composed  of  cellu- 
lose; while  the  walls  of  medullary  ray  cells  occurring  in  woods 
are  frequently  lignified. 

There  is  a  great  variation  in  the  character  of  the  cell  con- 
tents of  medullary  rays.  In  white  pine  bark  (Plate  48,  Fig. 
Bi)  are  deposits  of  tannin;  in  quassia  wood,  starch;  in  canella 
alba,  rosette  crystals  of  calcium  oxalate,  etc. 

LATEX  TUBES 

Living  latex  tubes,  like  sieve  tubes,  have  a  layer  of  proto- 
plasm lining  the  walls,  and,  in  addition,  have  numerous  nuclei. 
In  drug  plants  the  nuclei  are  not  distinguishable,  but  the  proto- 
plasm is  always  clearly  discernible. 

Latex  tubes  function  both  as  storage  and  as  conducting  cells. 
They,  like  the  sieve  tubes,  contain  proteid  substances  chiefly, 
yet  frequently  starch  is  found.  The  cells  bordering  the  latex 
tubes  absorb  from  them,  as  needed,  the  soluble  food  material. 
While  our  knowledge  concerning  the  function  of  latex  in  some 


PLATE  48 


A.  Cross-section  of  kava-kava  root  (Piper  methysticum,  Forst.,  f.)« 

1.  Unequal  diameter  medullary  ray  cells. 

2.  Vessels. 

3.  Wood  parenchyma. 

4.  Wood  fibres. 

B.  Cross-section  of  white  pine  bark  (Pinus  strobus,  L.). 

1.  Wavy  medullary  rays  with  tannin. 

2.  Parenchyma  cells. 

3.  Sieve  cells. 


144  HISTOLOGY   OF   MEDICINAL   PLANTS 

plants  is  meagre,  still  in  other  plants  it  is  practically  certain 
that  the  latex  is  composed  of  nutritive  substances  which  are 
utilized  by  the  plant  as  food.  In  certain  other  plants  the  latex 
appears  to  be  used  as  a  means  of  resisting  insect  attacks  and  as 
a  protection  against  injury. 

There  are  two  types  of  latex  tubes  common  to  plants,  namely, 
latex  cells  and  latex  vessels.  Latex  tubes  developing  from  a 
single  cell  do  not  differ  materially  from  a  latex  tube  originating 
from  the  fusion  of  several  cells.  In  each  case  the  latex  tube 
branches  to  such  an  extent  that  it  bears  no  resemblance  to  or- 
dinary cells.  It  would  seem  that  the  ultimate  branches  are  formed 
and  develop  in  much  the  same  manner  as  root  hairs — that  is, 
by  a  growing  tip  of  the  branch.  A  mature  plant  may  therefore 
have  latex  tubes  with  almost  numberless  branches  (Plate  50, 
Fig.  i)  and  be  of  very  great  length. 

The  branches  of  latex  tubes  develop  in  such  an  irregular 
manner  that  it  is  possible  to  obtain  a  cross  and  a  longitudinal 
section  of  the  latex  tubes  by  making  a  cross-section  of  stem. 
Such  a  section  is  shown  in  the  drawing  of  the  cross-section  of 
the  rhizome  of  black  Indian  hemp  (Plate  49,  Fig.  B). 

The  color  of  the  latex  in  medicinal  plants  varies  from  a 
gray  white  in  papaw  (carica  papaya),  aromatic  sumac,  black 
Indian  hemp,  and  bitter  root,  to  white  in  the  opium  poppy, 
light  orange  in  celandine,  and  deep  orange  in  bloodroot  (Plate 
50,  Fig.  2).  In  each  of  these  cases  it  is  the  latex  which  yields 
the  important  medicinal  products. 

PARENCHYMA 

The  larger  amount  of  plant  tissue  is  composed  of  parenchyma 
cells.  These  cells  vary  from  square  to  oblong,  or  they  may  be 
irregular  and  branched.  The  end  walls  are  square  or  blunt, 
and  the  wall  is  composed  of  cellulose,  with  the  exception  of  the 
wood  parenchyma,  which  has  lignified  walls. 

There  are  seven  characteristic  types  of  parenchyma  cells: 
(i)  cortical  parenchyma,  (2)  pith  parenchyma,  (3)  wood  par- 
enchyma, (4)  leaf  parenchyma,  (5)  aquatic  plant  parenchyma, 
(6)  endosperm  parenchyma,  (7)  phloem  parenchyma. 

Parenchyma  cells,  cortical,  pith,  aquatic  plant,  leaf,  flower, 


PLATE   49 


A.  Cross-section  of  black  Indian  hemp  (Apocynum  cannabinum,  L.). 

1.  Longitudinal  section  of  a  latex  tube. 

2.  Cross-section  of  latex  tube. 

3.  Parenchyma. 

B.  Cross-section  of  a  part  of  black  Indian  hemp  root. 

4.  Cross-section  of  a  large  latex  tube. 

5.  Parenchyma. 


PLATE   50 


LATEX  VESSELS 

1.  Radial-longitudinal   section   of  dandelion   root    (Taraxacum   officinale, 
Weber). 

2.  Cross-section  of  sanguinaria  root  (Sanguinaria  canadensis,  L.). 

3.  Cross-section  of  dandelion  root. 


CONDUCTING   TISSUE  147 

and  endosperm,  conduct  in  all  directions — upward,  downward, 
and  laterally.  The  direction  of  conduction  depends  upon  the 
needs  of  the  different  cells  forming  the  plant.  The  fluids  pass 
from  the  cell  with  an  abundance  of  cell  sap  to  the  cell  with  less 
cell  sap.  In  this  wall  all  cells  are  provided  with  food. 

Parenchyma  cells  conduct  water  absorbed  by  the  roots  and 
soluble  carbohydrate  material  chiefly. 

The  walls  of  all  the  different  types  of  parenchyma  cells  are 
composed  of  cellulose  with  the  exception  of  the  wood  parenchyma 
cells,  the  walls  of  which  are  lignified.  The  end  walls  of  non- 
branched  parenchyma  cells  and  the  cell  terminations  of  branched 
cells  are  very  blunt. 

CORTICAL  PARENCHYMA 

Cortical  parenchyma  (Plate  51)  differs  greatly  in  size,  thick- 
ness of  the  walls,  and  arrangement.  A  study  of  the  longitudinal 
sections  of  different  parts  of  medicinal  plants  reveals  the  fact 
that  the  cortical  parenchyma  cells  form  superimposed  layers 
in  which  the  end  walls  are  either  parallel,  in  which  case  the 
arrangement  resembles  that  of  several  rows  of  boxes  standing 
on  end,  or  the  end  walls  of  the  cells  alternate  with  each  other, 
in  which  case  the  arrangement  is  similar  to  that  of  the  arrange- 
ment of  the  bricks  in  a  building. 

In  certain  plants  the  cortical  parenchyma  cells  are  long  and 
narrow  and  rectangular  in  shape,  while  in  other  plants  the  cells, 
although  still  rectangular  in  outline,  are  very  broad  and  ap- 
proach the  square  form. 

All  typical  cortical  parenchyma  cells  have  uniformly  thick- 
ened non-pitted  walls.  In  most  barks  the  parenchyma  cells 
beneath  the  bark  are  elongated  tangentially,  but  are  very  narrow 
radially.  The  cells  are  always  arranged  around  intercellular 
spaces,  which  vary  from  triangular,  quadrangular,  etc.,  accord- 
ing to  the  number  of  cells  bordering  the  intercellular  space. 

PITH  PARENCHYMA 

Pith  parenchyma  (Plate  52)  differs  from  cortical  parenchyma 
cells  chiefly  in  the  character  of  the  walls,  which  are  usually  thicker 
and  always  pitted. 


PLATE  51 


PARENCHYMA  CELLS 

i.  Longitudinal  section  of  the  cortical  parenchyma  of  celandine  root 
(Chelidonium  majus,  L.)  2.  Cross-section  of  the  cortical  parenchyma  of 
sarsaparilla  root  (Smilax  ojficinalis,  Kunth). 


PLATE  52 


A.  Longitudinal  section  of  the  pith  parenchyma  of  grindelia  stem  (Grin- 
delia  squarrosa,  [Pursh]  Dunal). 

1.  Cell  cavity. 

2.  Cross-section  of  the  porous  end  wall. 

3.  Surface  view  of  the  porous  side  wall. 

B.  Cross-section  of  the  pith  parenchyma  of  grindelia  stem. 

1.  Cell  cavity. 

2.  Porous  walls. 

3.  Pitted  end  walls 


150  HISTOLOGY   OF  MEDICINAL   PLANTS 

LEAF  PARENCHYMA 

The  parenchyma  cells  (Plate  109,  Fig.  i)  of  leaves,  of  flower 
petals,  and  the  parenchyma  cells  of  some  aquatic  plants  are 
branched;  that  is,  each  cell  has  more  than  two  cell  terminations. 
These  cell  terminations  are  frequently  quite  attenuated  and 
usually  very  blunt.  Such  a  cell  structure  provides  for  a  greater 
amount  of  intercellular  space  and  a  maximum  exposure  of  sur- 
face. This  arrangement  makes  it  possible  for  the  parenchyma 
cells  of  the  leaf  to  absorb  more  readily  the  enormous  amount 
of  carbon  dioxide  needed  in  the  photosynthetic  process. 

AQUATIC  PLANT  PARENCHYMA 

The  parenchyma  of  aquatic  plants  (Plate  59)  has  large 
intercellular  spaces  formed  by  the  chains  of  cells. 

WOOD   PARENCHYMA 

Wood  parenchyma  (Plate  105,  Fig.  3)  cells  are  the  narrowest 
parenchyma  cells  occuring  in  the  plant.  Their  walls  are  always 
lignified  and  strongly  pitted,  and  in  some  cases  the  end  walls 
common  to  two  cells  are  obliquely  placed. 

PHLOEM  PARENCHYMA 

Phloem  parenchyma  (Plate  100,  Fig.  8)  cells  are  usually 
associated  with  sieve  cells.  They  are  very  long,  narrow,  and 
have  thin,  non-pitted  walls.  The  thinness  of  the  walls  un- 
doubtedly enables  the  cells  to  conduct  diffusible  food  substance 
more  quickly  than  the  cortical  parenchyma  cells. 

PALISADE    PARENCHYMA 

Palisade  parenchyma  of  leaves  is  of  the  typical  parenchyma 
shape  and  the  end  walls  are  placed  nearly  on  a  plane,  even 
when  more  than  one  layer  is  present.  The  cells  are  verv  small, 
however,  and  the  walls  are  very  thin  and  non-pitted. 


CHAPTER  VI 

AERATING  TISSUE 

The  aerating  tissue  of  the  plant  performs  a  threefold  func- 
tion: first,  it  permits  the  exchange  of  gases  during  photo- 
synthesis; secondly,  it  permits  the  entrance  of  oxygen  and  the 
exit  of  carbon  dioxide  during  respiration ;  and,  thirdly,  it  permits 
the  exit  of  the  excess  of  water  absorbed  by  the  plant. 

The  above  functions  are  carried  on  by  the  stomata,  the 
water-pores,  the  lenticels,  and  the  intercellular  spaces  of  the 
plant.  The  stoma  functions  as  the  chief  channel  for  the  passage 
of  CO2-laden  air  into  the  leaf  and  of  oxygen-laden  air  from  the 
leaf  to  the  atmosphere.  The  stoma  also  functions  as  an  organ 
of  transpiration,  since  through  the  stoma  a  large  part  of  the 
excess  water  of  the  plant  passes  off  into  the  air. 

WATER-PORES 

In  certain  plants  the  primary  epidermis  is  provided  with 
openings  resembling  stomata,  but  unlike  stomata  the  orifice 
remains  open,  and  instead  of  being  located  on  the  upper  or 
lower  surface  of  the  leaf,  they  are  located  on  the  margin  of 
leaves  immediately  outward  from  the  veins.  Water  is  given 
off  to  the  atmosphere  from  these  openings.  Such  an  opening 
is  usually  designated  as  a  water-pore. 

STOMATA 

The  chief  external  openings  of  the  epidermis  of  leaves,  of 
herbs,  and  of  young  wood  stems  are  known  as  stomata.  Sur- 
rounding the  stoma  are  two  cells  known  as  guard  cells. 

Guard  cells  differ  greatly  in  form,  in  size,  in  arrangement, 
in  occurrence,  in  association,  in  abundance  (Plates  53,  54,  and 
55),  and  in  color.  The  guard  cells  surrounding  the  stoma  vary 
in  form  from  circular  to  lens-shaped.  In  most  leaves  the  outiine 

151 


PLATE  53 


3 


1.  Stoma  and  surrounding  cells  of  aconite  stem  (Aconitum  napellus,  L.). 

2.  Stoma  and  angled  striated  walled  surrounding  cells  of  peppermint  stem 
(Mentha  piperita,  L.).       3.  Stoma  and  elongated  surrounding  cells  of  lobelia 
stem  (Lobelia  inflate,  L.). 


PLATE  54 


TYPES  OF  STOMA 

1.  Under  epidermis  of  short  buchu  (Barosma  betvlina,  [Berg.]  Battling  and 
Wendl.,  f.)  showing  stoma  and  deposits  of  hesperidin. 

2.  Under  epidermis  of  Alexandria  senna  (Cassia  acutifolia,  Delile)  showing 
stoma  and  thick-angled  walled  surrounding  cells. 

3.  Upper  epidermis  of  eucalyptus  leaf  (Eucalyptus  globulus,  Labill.)  show- 
ing sunken  stoma  and  slightly  beaded  walled  surrounding  cells. 

4.  Under  epidermis  of  belladonna  leaf   (Atropa  belladonna,  L.)  showing 
stoma  and  wavy,  striated,  walled  epidermal  cells. 


154  HISTOLOGY   OF   MEDICINAL   PLANTS 

of  the  guard  cells  is  rounded  or  has  a  curved  outline;  but  in  a 
few  cases  the  guard  cells  have  angled  outlines. 

The  arrangement  of  the  surrounding  cells  of  the  stoma 
is  one  of  the  most  important  characteristics  of  the  different 
leaves.  As  a  rule  the  number  of  surrounding  cells  about  a 
stoma  is  constant  for  a  given  species.  In  senna  leaves  (Plate 
54,  Fig.  2)  there  are  normally  two  surrounding  cells  about 
each  guard  cell,  while  in  coca  there  are  four  (Plate  55,  Fig.  i). 
In  senna  the  long  diameter  of  the  surrounding  cells  is  parallel  to 
the  long  diameter  of  the  guard  cells ;  but  in  coca  the  long  diameter 
of  two  surrounding  cells  is  at  right  angles  to  the  long  diameter  of 
the  guard  cells,  while  two  cells  are  parallel  to  the  long  diameter 
of  the  guard  cells. 

In  most  leaves  there  are  more  than  two  cells  around  the 
guard  cells. 

The  form  and  size  of  the  surrounding  cells  must  always  be 
considered.  In  most  leaves  they  are  variable  in  size  and  form. 

Guard  cells  occur  first,  even  with  the  surface  of  the  leaf  (Plate 
56,  Fig.  A);  secondly,  above  the  surface  of  the  leaf  (Plate  56, 
Fig.  B) ;  and,  thirdly,  below  the  surface  of  the  leaf.  (Plate  56, 
Fig.  C).  Only  one  of  the  above  types  occurs  in  a  given  species 
of  plant.  That  is,  plants  with  stomata  above  the  surface  of  the 
leaf  do  not  have  stomata  on  a  level  with  or  below  the  leaf 
surface. 

The  number  of  stomata  on  a  given  surface  of  a  different  leaf 
varies  considerably. 

In  many  of  the  medicinal  leaves  stomata  occur  only  on  the 
under  surface  of  the  leaf.  In  other  leaves  stomata  occur  on  both 
surfaces  of  the  leaf;  but  in  such  cases  there  are  a  greater  number 
on  the  under  surface. 

In  certain  leaves  the  long  diameter  of  the  guard  cells  is 
parallel  to  the  length  of  the  leaf;  in  other  cases  the  long  diameter 
of  the  stoma  is  arranged  at  right  angles  to  the  length  of  the  leaf. 

In  other  leaves  the  arrangement  is  still  more  irregular,  the 
guard  cells  assuming  all  sorts  of  positions  in  relation  to  the 
length  of  the  leaf. 

The  relation  of  the  stoma  to  surrounding  cells  is  best  shown 
in  cross-sections  of  the  leaf.  In  powders  the  relationship  of 
the  stoma  to  the  surrounding  cells  is,  however,  readily  ascer- 


PLATE  55 


LEAF  EPIDERMI  WITH  STOMA 

1.  Under  epidermis   of  coca  leaf  (Erythroxylon  coca,  Lam.)  with  stoma  on 
a  level  with  the  surface. 

2.  Under  epidermis  of  false  buchu  (Marrubium  peregrinum,  L.)  with  stoma 
below  the  level  of  the  surface. 

3.  Upper  epidermis  of  deer  tongue   (Trilisia  odoratissima,  [Walt.]  Cass.) 
with  stoma  above  the  leaf  surface. 


PLATE  56 


A.  Cross-section  of  belladonna  leaf  (Atropa  belladonna,  L.).  I,  Epidermal 
cells;  2,  Guard  cells  even  with  the  leaf  surface;  3,  Surrounding  cells;  4,  Air 
space  below  the  guard  cells;  5,  Palisade  cells;  6,  Mesophyll  cells.  B.  Cross- 
section  of  deer  tongue  leaf.  I,  Epidermal  cells;  2,  Guard  cells  above  the  sur- 
face of  the  leaf;  3,  Surrounding  cells;  4,  Air  space  below  the  guard  cells; 
5,  Hypodermal  cells.  C.  Cross-section  of  white  pine  leaf  (Pinus  strobus,  LJ. 
i,  Epidermal  and  hypodermal  cells;  2,  Guard  cells  below  the  leaf  surface; 
3,  Surrounding  cells;  4,  Air  space  below  the  guard  cells;  5,  Parenchyma  cells 
with  projecting  inner  walls. 


AERATING  TISSUE  157 

tained.  If  the  guard  cells  come  in  focus  first,  they  are  above 
the  surface;  if  the  guard  cells  and  the  surrounding  cells  come 
in  focus  at  the  same  time,  the  stomata  are  even  with  the  sur- 
face; if  the  stomata  come  in  focus  after  the  surrounding  cells, 
they  are  below  the  surface  of  the  leaf.  The  relationship  of 
the  stoma  to  the  surrounding  cells  should  always  be  ascertained, 
not  only  in  cross-sections  of  the  leaf,  but  also  in  powders. 

There  is  the  greatest  possible  variation  in  the  size  of  guard 
cells.  Phis  fact  must  always  be  kept  in  mind  when  studying 
leaves.  This  variation  in  the  size  of  the  guard  cells  is  clearly 
illustrated  by  coca,  senna,  and  by  deer's-tongue.  In  coca  the 
stomata  are  very  small;  in  senna  they  are  larger;  while  in 
deer's-tongue  the  stomata  are  very  large. 

The  width  and  length  of  the  stoma  or  opening  between  the 
guard  cells  are  of  a  character  which  must  not  be  overlooked. 
Generally  speaking,  those  leaves  which  have  large  guard  cells 
will  have  correspondingly  large  stomata. 

The  guard  cells  usually  contain  chloroplasts  showing  various 
stages  of  decomposition. 

In  bay-rum  leaf  the  guard  cells  are  of  a  bright  reddish- 
brown  color,  but  in  most  leaves  the  guard  cells  are  colorless. 

LENTICELS 

Lenticels  are  small  openings  occurring  in  the  bark  of  plants. 
The  lenticels  bear  the  same  relationship  to  the  stem  that  the 
stomata  do  to  the  leaves.  Lenticels,  like  stomata,  have  a  three- 
fold function — namely,  exchange  of  gases  in  photosynthesis, 
in  respiration,  and  the  giving  off  of  water. 

Lenticels  are  macroscopically  as  well  as  microscopically 
important.  When  unmagnified  the  lenticels  are  circular,  lens- 
shaped,  or  irregular  in  outline.  They  are  arranged  in  parallel 
longitudinal  lines  or  parallel  transverse  lines,  or  they  are  ir- 
regularly scattered.  The  latter  is  the  usual  arrangement.  In 
most  cases  they  are  elevated  slightly  above  the  surface  of  the 
bark.  In  root  barks  particularly  the  lenticels  stand  out  promi- 
nently from  the  surface  of  the  bafk  and  in  many  cases  appear 
stalked. 

The  color  of  the  lenticels  differs  greatly  in  the  different 


158  HISTOLOGY   OF   MEDICINAL   PLANTS 

plants.  In  acer  spicatium  they  are  brown;  in  witch-hazel  they 
are  gray;  in  xanthoxylium  they  are  yellowish;  and  lastly,  the 
number  of  lenticels  occurring  in  a  given  surface  of  the  bark 
should  always  be  considered. 

On  cross-sections  the  lenticel  (Plate  57,  Fig.  2)  is  seen  to 
have  a  central  depressed  portion  maole  up  of  loosely  arranged 
cells.  Bordering  the  cavity  are  typical  cork  cells.  The  cork 
cells  immediately  surrounding  the  lenticels  are  usually  darker 
in  color,  and  many  of  the  cells  are  partly  broken  down. 

The  size  of  lenticels  will  vary  according  to  the  type  of  the 
lenticel.  In  studying  sections  more  attention  should  be  paid 
to  the  character  of  the  cells  forming  the  lenticels  than  to  the 
size  of  the  lenticel. 

On  cross-section  the  intercellular  spaces  (Plate  58)  are  tri- 
angular, quadrangular,  or  irregular.  The  spaces  between  equal 
diameter  parenchyma  cells  is  triangular  if  three  cells  surround 
the  space,  and  quadrangular  if  four  cells  surround  the  space, 
etc.  These  spaces  are  in  direct  contact  with  similar  spaces  that 
traverse  the  tissue  at  right  angles  to  its  long  axis. 

The  branched  mesophyll  cells  of  the  leaf  and  aquatic  plant 
parenchyma  (Plate  59)  are  arranged  around  irregular  cavities. 
In  leaves  and  aquatic  plants  these  spaces  run  parallel  to  the 
long  axis  of  the  organ. 

In  each  of  the  above  cases  the  cavity  is  formed  by  the  sepa- 
ration of  the  cell  walls.  There  is  still  another  type  of  irregular 
cavities  which  is  formed  by  the  dissolution  or  tearing  apart  of 
the  cell  walls.  Such  cavities  are  found  in  the  stems  and  roots 
of  many  herbs. 

The  pith  cells  in  the  stems  of  many  herbs  become  torn 
apart  during  the  growth  of  the  stem,  with  the  result  that  large 
irregular  cavities  are  formed.  These  cavities  are  usually  filled 
with  circulatory  air. 

In  the  stems  of  conium,  cicuta,  angelica,  and  other  larger 
herbaceous  stems  the  pith  separates  into  layers.  When  a 
longitudinal  section  is  made  of  such  a  stem  it  is  seen  to  be  com- 
posed of  alternating  air  spaces  and  masses  of  pith  parenchyma. 

The  intercellular  spaces  are  very  large  in  leaves  where 
enormous  quantities  of  carbon  dioxide  are  vitalized  in  photo- 
synthesis. 


PLATE   57 


PLATE  58 


INTERCELLULAR  AIR  SPACES 

A.  Cross-section  of  uva-ursi  leaf  (Arctostaphylos  uva-ursi,  [L.]  Spreng.). 
i.  Irregular  intercellular  air  spaces. 

B.  Cross-section  of  the  cortical  parenchyma  of  sarsaparilla  root  (Smilax 
officinalis,  Kunth).       i,  Triangular  intercellular  spaces;   2,  Quadrangular  in- 
tercellular air  spaces;  3,  Pentagular  intercellular  air  spaces- 


IRREGULAR  INTERCELLULAR  AIR  SPACES 

1.  Skunk-cabbage  (Symplocarpus  fcetidus,  [L.]  Nutt.) 

2.  Calamus  rhizome  (Acorus  calamus,  L.). 


162  HISTOLOGY   OF   MEDICINAL   PLANTS 

In  the  rhizome  of  calamus  and  other  aquatic  plants  the 
intercellular  spaces  are  very  large.  The  cells  of  these  plants 
are  arranged  in  the  form  of  branching  chains  of  cells  which  thus 
provide  for  large  intercellular  spaces. 

The  cells  of  the  middle  layer  of  flower  petals,  like  the  meso- 
phyll  of  leaves,  is  loosely  arranged  owing  to  the  peculiar  branch- 
ing form  of  the  cells. 

Seeds  and  fruits  contain,  as  a  rule,  few  or  no  intercellular 
spaces, 


CHAPTER  VII 

SYNTHETIC  TISSUE 

Under  synthetic  tissue  are  grouped  all  tissues  and  cells  which 
form  substances  or  compounds  other  than  protoplasm.  Such 
compounds  are  stored  either  in  special  cavities  or  in  the  cells 
of  the  plant,  as  the  glandular  hairs;  internal  secreting  cavities 
of  barks,  stems,  leaves,  fruits,  seeds,  and  flowers;  photosyn- 
thetic  cells  or  cells  with  chlorophyll,  and  the  parenchymatic 
cells  which  form  starch,  sugar,  fats,  alkaloids,  etc. 

PHOTOSYNTHETIC   TISSUE 

.The  most  important  non-glandular  synthetic  tissue  is  the 
photosynthetic  tissue,  which  is  composed  of  the  chlorophyll- 
bearing  cells  of  the  plant.  These  are  the  so-called  green  cells 
of  leaves,  of  stems  of  herbs,  of  young  woody  stems,  and  in  the 
older  woody  stems  of  plants  like  wild  cherry,  birch,  etc.  The 
greater  part  of  the  tissue  of  leaves  is  composed  of  chlorophyll- 
bearing  cells. 

Leaves  collectively  constitute  the  greatest  synthetic  manu- 
facturing plant  in  the  world,  because  the  green  cells  of  the  leaf 
produce  most  of  the  food  of  men  and  animals.  The  two  com- 
pounds utilized  in  the  manufacture  of  food  are  carbon  dioxide 
(CO2)  and  water  (H2O).  These  two  compounds  are  combined 
by  chlorophyll  through  the  agency  of  light  into  starch.  Chemi- 
cally this  reaction  may  be  expressed  as  follows:  , 

6CO2  +  sH2O  =  2C6H1<A  +  6O2. 

During  the  day  a  large  quantity  of  starch  is  formed.  At 
night  through  the  action  of  a  ferment  the  excess  of  starch  remain- 
ing in  the  leaf  is  converted  into  sugar  (C6Hi206)  —  CoH10O5  + 
H2O  =  C6Hi2O6.  In  this  form  it  is  distributed  to  the  living 
cells  of  the  plant.  The  presence  or  absence  of  starch  in  leaves 
is  easily  ascertained  by  placing  the  leaf  in  hot  alcohol  to  remove 

163 


164  HISTOLOGY  OF  MEDICINAL  PLANTS 

the  chlorophyll,  and  by  adding  LugoPs  solution.  If  starch  is 
present,  the  contents  of  the  cells  will  become  bluish  black;  but 
if  no  starch  is  oresent,  the  cells  remain  colorless. 

GLANDULAR  TISSUE 

The  glandular  tissue  of  the  plant  is  divided  into  two  groups, 
according  to  where  it  occurs.  These  groups  are,  first,  external 
glandular  tissue,  and  secondly,  internal  glandular  tissue.  The 
most  important  external  glandular  tissue  is  composed  of  the 
glandular  hairs.  These  are  divided  into  two  groups:  first, 
unicellular;  and  secondly,  multicellular  glandular  hairs. 

UNICELLULAR  GLANDULAR  HAIRS 

The  unicellular  glandular  hairs  are  either  sessile  or  stalked. 

Sessile  unicellular  hairs  occur  in  digitalis  leaves. 

Stalked  unicellular  hairs  of  digitalis  are  shown  on  Plate  60, 
Fig.  2. 

Unicellular  uniseriate  stalked  glandular  hairs  occur  on  the 
stems  of  the  common  house  geranium  (Plate  61,  Fig.  2),  on  the 
leaves  of  butternut,  the  leaves  and  stems  of  marrubium  peregri- 
num  (Plate  98,  Fig.  5),  and  in  arnica  flowers.  The  stalk  varies 
from  two  to  ten  cells;  in  eriodictyon  the  cells  vary  from  four 
to  eight  cells. 

Unicellular  multiseriate  stalked  glandular  hairs  are  not  of 
common  occurrence. 

MULTICELLULAR  GLANDULAR  HAIRS 

Multicellular  glandular  hairs  are  divided  into  two  groups: 
first,  sessile;  and  secondly,  stalked  hairs. 

% Multicellular  sessile  glandular  hairs  occur  on  the  leaves  of 
peppermint  (Plate  60,  Fig.  3),  horehound  (Plate  97,  Fig.  7), 
and  in  hops  (Plate  60,  Fig.  4).  In  each  of  these  hairs  there  are 
eight  secretion  cells. 

Stalked  glandular  hairs  are  divided  into  two  groups:  first, 
uniseriate  stalked;  and  secondly,  multiseriate  stalked  glandular 
hairs. 

Multicellular  uniseriate  stalked  glandular  hairs  occur  on 
the  leaves  of  tobacco  (Plate  61,  Fig.  4),  belladonna  (Plate  61, 


PLATE  60 


GLANDULAR  HAIRS 

1.  Kamala  (Mallotus  philippinensis ,  [Lam.]  [Muell.]  Arg.). 

2.  Digitalis  leaf  (Digitalis  purpurea,  L.). 

3.  Peppermint  leaf  (Mentha  piperita,  L.). 

4.  Lupulin. 

5.  Cannabis  indica  leaf  (Cannabis  saliva,  L.). 


166  HISTOLOGY   OF   MEDICINAL  PLANTS 

Fig.  i),  and  digitalis  (Plate  60,  Fig.  2),  and  of  the  fruit  of  rhus 
glabra. 

Multicellular  multiseriate  stalked  glandular  hairs  occur  on 
the  stems  and  leaves  of  cannabis  indica  (Plate  60,  Fig.  5). 

In  the  glandular  hair  of  kamala  (Plate  60,  Fig.  i)  the  num- 
ber of  secretion  cells  is  variable  and  papillate  in  form,  and  the 
cuticle  is  separated  from  the  secretion  cells. 

In  the  glandular  hair  of  hops  the  outer  wall  or  cuticle  is  torn 
away  from  the  secretion  cells,  and  the  cavity  thus  formed  serves 
as  a  storage  cavity.  This  distended  cuticle  of  the  hops  shows 
the  outline  of  the  cells  from  which  it  was  separated, 

In  the  glandular  hairs  of  the  mints  the  secreted  products 
(volatile  oils)  are  stored  between  the  secretion  cells  and  the  outer 
detached  cuticle.  This  cuticle  is  elastic,  and  it  becomes  greatly 
distended  as  the  volatile  oil  increases  in  amount. 

In  many  of  the  so-called  glandular  hairs,  tobacco,  belladonna 
geranium,  etc.,  the  synthetic  products  are  retained  in  the  glandu- 
lar cells,  there  being  no  special  cavity  for  their  storage. 

These  hairs  usually  contain  an  abundance  of  chlorophyll. 

The  division  wall  of  multicellular  glandular  hairs  may  be 
vertical,  as  in  the  two-celled  hair  of  digitalis  (Plate  60,  Fig.  2) ; 
as  in  horehound  (Plate  97,  Fig.  6),  and  as  in  peppermint  (Plate 
60,  Fig.  3);  in  this  case  there  are  eight  cells,  and  they  form  a 
more  or  less  flat  plate  of  cells. 

In  other  hairs  the  division  wall  is  horizontal;  this  produces 
a  chain  of  superimposed  secreting  cells,  as  in  some  of  the  gland- 
ular hairs  of  belladonna  leaf  (Plate  61,  Fig.  i),  etc. 

In  other  hairs  the  division  walls  are  both  vertical  and  hori- 
zontal, as  in  tobacco  (Plate  61,  Fig.  4),  henbane  (Plate  61,  Fig. 
3),  belladonna  (Plate  61,  Fig.  i). 

Other  characters  to  be  kept  in  mind  in  studying  glandular 
hairs  are  the  following:  Color  of  cell  contents;  size  of  the 
cells,  whether  uniform  or  variable;  character  of  wall,  whether 
smooth  or  rough. 

SECRETION   CAVITIES 

Secretion  cavities  are  divided  into  three  groups,  according 
to  the  nature  of  the  origin  of  the  cavity:  first,  schizogenous 
cavities,  which  originate  by  a  separation  of  the  walls  of  the 


PLATE   61 


STALKED  GLANDULAR  HAIRS 

1.  Belladonna  leaf  (Atropa  belladonna,  L.). 

2.  Geranium  stem  (Geranium  maculatum,  L.), 

3.  Henbane  leaf  (Hyoscyamus  niger,  L.). 

4.  Tobacco  leaf  (Nicotiana  tabacum,  L.). 


1(58  HISTOLOGY  OF  MEDICINAL  PLANTS 

secretion  cells;  secondly,  lysigenous  cavities,  which  arise  by  the 
dissolution  of  the  walls  of  centrally  located  secretion  cells;  and 
thirdly,  schizo-lysigenous  cavities,  which  originate  schizogen- 
ously,  but  later  become  lysigenous  owing  to  the  dissolution  of 
the  outer  layers  of  the  secretion  cells. 

SCHIZOGENOUS  CAVITIES 

Schizogenous  cavities  occur  in  white  pine  bark  (Plate  62, 
Fig.  B).  The  cells  lining*the  cavity  are  mostly  tangentially  elon- 
gated, and  the  wall  extends  into  the  cavity  in  the  form  of  a 
papillate  projection.  Immediately  back  from  these  cells  are 
two  or  three  layers  of  cells  which  resemble  cortical  parenchyma 
cells,  except  that  they  are  smaller  and  their  walls  are  thinner. 

'In  white  pine  bark  there  is  a  single  layer  of  thin-walled 
cells  lining  the  cavity.  Immediately  surrounding  the  secretion 
cells  is  a  single  layer  of  thick- walled  fibrous  cells. 

In  klip  buchu  (Plate  63,  Fig.  B),  as  in  white  pine  leaf  (Plate 
64,  Fig.  B),  there  is  a  single  layer  of  thin-walled  secretion  cells 
which  are  surrounded  on  three  sides  with  parenchyma  cells  and 
on  the  outer  side  by  epidermal  cells. 

LYSIGENOUS   CAVITIES 

Lysigenous  cavities  occur  on  the  rind  of  citrus  fruits — bitter 
and  sweet  orange,  lemon,  grapefruit,  lime,  etc.,  and  in  the  leaves 
of  garden  rue,  etc. 

In  bitter  orange  peel.  (Plate  64,  Fig.  A)  the  cavity  is  very 
large,  and  the  cells  bordering  the  cavity  are  broken  and  partially 
dissolved.  The  entire  cells  back  of  these  are  white,  thin- walled, 
tangentially  elongated  cells.  There  is  a  great  variation  in  the 
size  of  these  cavities,  the  smaller  cavities  being  the  recently 
formed  cavities. 

SCHIZO-LYSIGENOUS  CAVITIES 

Schizo-lysigenous  cavities  are  formed  in  white  pine  bark 
and  many  other  plants  owing  to  the  increase  in  diameter  of  the 
stem.  In  such  cases  the  walls  of  the  secreting  cells  break  down. 
The  resulting  cavity  resembles  lysigenous  cavities. 

Unicellular  secretion  cavities  occur  in  ginger,  aloe,  calamus, 
and  in  canella  alba  barb. 


PLATE  62 


A.  Cross-section  of  calamus  rhizome"  (Acorus  calamus,  L.).  I,  Intercel- 
lular space;  2,  Parenchyma  cells;  3,  Secretion  cavity.  B.  Cross-section  of 
white  pine  bark  (Pinus  strobus,  L.).  I,  Parenchyma;  2,  Secretion  cavity; 
3,  Secretion  cells. 


PLATE  63 


L-J 


X.  Cross-section  of  a  portion  of  canella  alba  bark  (Canella  alba,  Murr.), 

I.  Excretion  cavity. 
B.  Cross-section  of  a  portion  of  klip  buchu  leaf. 

1.  Epidermal  cells. 

2.  Secretion  cavity. 

3.  Secretion  cells. 


PLATE  64 


A.  Cross-section  of  bitter  orange  peel  (Citrus  aurantium,  amara,  L.). 
I,  Internal  secretion  cavity  formed  by  the  dissolution  of  the  walls  of  the  central 
secreting  cells;  2,  Secretion  cells.  B.  Cross-section  of  white  pine  leaf  (Finns 
strobus,  L.).  I,  Epidermal  and  hypodermal  cells;  2,  Parenchyma  cells  with 
protuding  inner  walls;  3,  Endodermis;  4,  Secretion  cavity;  5,  Secretion  cells. 


172  HISTOLOGY   OF   MEDICINAL  PLANTS 

In  calamus  (Plate  62,  Fig.  A)  the  cavity  is  larger  than  the 
surrounding  cells;  it  is  rounded  in  outline,  and  it  contains 
oleoresin.  These  cavities  are  in  contact  with  the  ordinary 
parenchyma  cells,  from  which  they  are  easily  distinguished  by 
their  larger  size  and  rounded  form. 

.The  unicellular  oil  cavity  of  canella  alba  (Plate  63,  Fig.  A) 
is  rounded  or  oval  in  cross-section  and  is  many  times  larger 
than  the  surrounding  cells.  The  wall,  which  is  very  thick,  is 
of  a  yellowish  color. 

Secretion  cavities  vary  greatly  in  form,  according  to  the 
part  of  the  plant  in  which  they  are  found.  In  flower  petals  and 
leaves  they  are  spherical;  in  barks  they  are  usually  elliptical; 
in  umbelliferous  fruits  they  are  elongated  and  tube-like. 

Mucilage  cavities  are  not  of  common  occurrence  in  medicinal 
plants.  They  occur,  however,  in  the  stem  and  root  bark  of 
sassafras,  the  stem  bark  of  slippery  elm,  the  root  of  althea,  etc. 


CHAPTER  VIII 

STORAGE  TISSUE 

Most  drug  plants  contain  storage  products  because  they 
are  collected  at  a  period  of  the  year  when  th^  plant  is  storing, 
or  has  stored,  reserve  products.  These  products  are  stored 
in  a  number  of  characteristic  ways  and  in  different  types  of 
tissue. 

The  most  important  of  the  different  types  of  storage  tissue 
that  occurs  in  plants  are  the  storage  cells,  the  storage  cavities, 
and  the  storage  walls. 

STORAGE  CELLS 

Several  different  types  of  cells  function  as  storage  tissue. 
These  cells,  which  are  given  in  the  order  of  their  importance, 
are  parenchyma,  crystal  cells,  medullary  rays,  stone  cells,  wood 
fibres,  bast  fibres,  and  epidermal  and  hypodermal  cells. 

• 

CORTICAL  PARENCHYMA 

Cortical  parenchyma  of  biennial  rhizomes,  bulbs,  roots, 
and  the  parenchyma  of  the  endosperm  of  seeds  store  most  of 
the  reserve  economic  food  products  of  the  higher  plants. 

Pith  parenchyma  of  sarsaparilla  root  (Plate  65,  Fig.  4)  and 
the  pith  parenchyma  of  the  rhizome  of  memspermun,  like  the 
pith  parenchyma  of  most  plants,  function  as  storage  cells. 

WOOD  PARENCHYMA 

Wood  parenchyma,  particularly  of  the  older  wood,  function 
as  storage  tissue.  The  wood  parenchyma  of  quassia,  like  the 
wood  parenchyma  of  most  woods,  contain  stored  products.  In 
some  cases  the  wood  parenchyma  contain  starch,  in  others  crys- 
tals, and  in  others  coloring  matter,  etc. 

In  many  plants,  however,  the  parenchyma  cells  contain 
crystals.  The  parenchyma  cells  of  rhubarb  contain  rosette 

173 


PLATE   65 


'Ol 
0 


6 


I.  Stone  cells  with  starch  of  Ceylon  cinnamon  (Cinnamomum  reylanicum, 
Nees.).  2.  Stone  cells  with  solitary  crystals  of  calumba  root  (Jateorhiza 
palmata,  [Lam.]  Miers).  3.  Parenchyma  cells,  with  starch  of  cascarilla  bark 
(Croton  eluteria,  [L.]  Benn.).  4.  Cortical  parenchyma  with  starch  of  sarsa- 
parilla  root  (Smilux  officinalis,  Kunth).  5.  Cortical  parenchyma,  with  starch 
of  leptandra  rhizome  (Leptandra  virgi-nica,  [L.]  Nutt.).  6.  Crystal  cells,  with 
solitary  crystals  of  quebracho  bark  (Schlechtendat).  7.  Bast  fibre  of  black- 
berry root  with  starch  (Rubus  cuneifolius,  Pursh.). 


PLATE   66 


MUCILAGE  AND  RESIN 

1.  Cross-section  of  elm  bark  (Ulmus  fulva,  Michaux)  showing  two  cavities 
filled  with  partially  swollen  mucilage. 

2.  Mucilage  mass  from  sassafras  stem  bark  (Sassafras  variifolium,  L.). 

3.  Mucilage  mass  from  elm  bark. 

4.  Resin  mass  from  white  pine  bark  (Finns  strobus,  L.). 


176  HJSTOLOGY   OF  MEDICINAL  PLANTS 

crystals,  while  the  parenchyma  cells  of  the  cortex  of  sarsaparilla 
and  false  unicorn  root  contain  bundles  of  raphides.  In  every  case 
observed  the  raphides  are  surrounded  by  mucilage.  This  is  true 
of  squills,  sarsaparilla,  false  unicorn,  etc.  When  cells  with 
raphides  and  mucilage  are  mounted  in  a  mixture  of  alcohol, 
glycerine,  and  water,  the  mucilage  first  swells  and  finally  dis- 
appears. 

STORAGE  CAVITIES 

Particular  attention  should  be  given  to  storage  cavities 
whenever  they  occur  in  plants,  for  the  reason  that  they  are 
usually  filled  with  storage  products,  and  for  the  added  reason 
that  storage  cavities  are  not  common  to  all  plants.  Storage 
cavities  occur  in  roots,  stems,  leaves,  flowers,  fruits,  and  seeds. 

CRYSTAL  CAVITIES 

Characteristic  crystal  cavities  occur  in  many  plants.  Such 
a  cavity  containing  a  bundle  of  raphides  is  shown  in  the  cross- 
section  of  skunk  cabbage  leaf  (Plate  67). 

« 

SECRETION  CAVITIES 

In  white  pine  bark  there  are  a  great  number  of  secretion 
cavities  which  are  partially  or  completely  filled  with  oleoresin. 
In  the  cross-sections  of  white  pine  bark  the  secretion  cavities 
are  very  conspicuous,  and  they  vary  greatly  in  size.  This 
variation  is  due,  first,  to  the  age  of  the  cavity,  the  more  re- 
cently formed  cavities  being  smaller;  and  secondly,  to  the 
nature  of  the  section,  which  will  be  longer  in  longitudinal  section, 
which  will  be  through  the  length  of  the  secretion  cavity,  and 
shorter  on  transverse  section.  Such  a  section  shows  the  width 
of  the  secretion  cavity. 

Characteristic  mucilage  cavities  occur  in  sassafras  root,  stem 
bark,  elm  bark  (Plate  66,  Fig.  i),  marshmallow  root,  etc. 
These  cavities  form  a  conspicuous  feature  of  the  cross-section 
of  these  plants.  The  presence  or  absence  of  mucilage  cavities 
in  a  bark  should  be  carefully  noted. 

LATEX   CAVITIES 

The  latex  tube  cavities  are  characteristic  in  the  plants  in 
which  they  occur.  These  cavities  as  explained  under  latex 
tubes  are  very  irregular  in  outline. 


CROSS-SECTION  OF  SKUNK-CABBAGE  LEAF  (Symplocarpus  fcetidus, 

[L.]  Nutt.) 

1.  Crystal  cavity. 

2.  Bundle  of  raphides. 


178  HISTOLOGY   OF   MEDICINAL   PLANTS 

OIL   CAVITY 

Canella  alba  contains  an  oil  cavity  resembling  in  form  the 
mucilage  cavity  of  elm  bark. 

Secretion  cavities  occur  in  most  of  the  umbelliferous  fruits. 
For  each  fruit  there  is  a  more  or  less  constant  number  of  cavities. 
Anise  has  twenty  or  more,  fennel  usually  has  six  cavities,  and 
parsley  has  six  cavities. 

In  poison  hemlock  fruits  there  are  no  secretion  cavities.  In 
certain  cases,  however,  the  number  of  secretion  cavities  can 
be  made  to  vary.  This  was  proved  by  the  author  in  the  case 
of  celery  seed.  He  found  that  cultivated  celery  seed,  from 
which  stalks  are  grown,  contains  six  oil  cavities  (Plate  122, 
Fig.  2),  while  wild  celery  seed  (Plate  102,  Fig.  i),  grown  for  its 
medicinal  value,  always  contains  more  than  six  cavities.  Most 
of  the  wild  celery  seeds  contain  twelve  cavities. 

Many  leaves  contain  cavities  for  storing  secreted  products. 
Such  storage  cavities  occur  in  fragrant  goldenrod,  buchu,  thyme, 
savary,  etc. 

The  leaves  in  which  such  cavities  occur  are  designated  as 
pellucid-punctate  leaves.  Such  leaves  will,  when  held  be- 
tween the  eye  and  the  source  of  light,  exhibit  numerous  rounded 
translucent  spots,  or  storage  cavities. 

GLANDULAR    HAIRS 

The  glandular  hair  of  peppermint  (Plate  60,  Fig.  3)  and  other 
mints  consists  of  eight  secretion  cells,  arranged  around  a  central 
cavity  and  an  outer  wall  which  is  free  from  the  secretion  cells. 
This  outer  wall  becomes  greatly  distended  when  the  secretion 
cells  are  active,  and  the  space  between  the  secretion  cells  and 
the  wall  serves  as  the  storage  place  for  the  oil.  When  the  mints 
are  collected  and  dried,  the  oil  remains  in  the  storage  cavity 
for  a  long  time. 

STONE  CELLS 

The  stone  cells  of  the  different  cinnamons  (Plate  65,  Fig.  i) 
store  starch  grains;  these  grains  often  completely  fill  the  stone  cells. 

The  yellow  stone  cells  of  calumba  root  (Plate  65,  Fig.  2) 
usually  contain  four  prisms  of  calcium  oxalate,  which  may  be 
nearly  uniform  or  very  unequal  in  size. 


STORAGE   TISSUE  179 

BAST  FIBRES 

The  bast  fibres  of  the  different  rubus  species  (Plate  65, 
Fig.  7)  contain  starch.  The  medullary  rays  of  quassia  (Plate 
107,  Fig.  2)  contain  starch;  while  the  medullary  rays  of  canella 
alba  contain  rosette  crystals.  In  a  cross-section  of  canella  alba 
(Plate  81,  Fig.  3)  the  crystals  form  parallel  radiating  lines  which, 
upon  closer  examination,  are  seen  to  be  medullary  rays,  in  each 
cell  of  which  a  crystal  usually  occurs. 

The  epidermal  and  hypodermal  cells  of  leaves  serve  as 
water-storage  tissue.  These  cells  usually  appear  empty  in  a 
section. 

The  barks  of  many  plants — i.e.,  quebracho,  witch-hazel, 
cascara,  frangula,  the  leaves  of  senna  and  coca,  and  the  root 
of  licorice — contain  numerous  crystals.  These  crystals  occur  in 
special  storage  cells — crystal  cells  (Plate  65,  Fig.  6) — which 
usually  form  a  completely  enveloping  layer  around  the  bast 
fibres.  These  cells  are  usually  the  smallest  cells  of  the  plant 
in  which  they  occur,  and  with  but  few  exceptions  each  cell 
contains  but  a  single  crystal. 

The  epidermal  cells  of  senna  leaves  and  the  epidermal  cells 
of  mustard  are  filled  with  mucilage;  the  walls  even  consist  of 
mucilage.  Such  cells  are  always  diagnostic  in  powders. 

STORAGE   WALLS 

Storage  walls  (Plates  68  and  69)  occur  in  colchicum  seed, 
saw  palmetto  seed,  areca  nut,  nux  vomica,  and  Saint  Ignatius's 
bean.  In  each  of  these  seeds  the  walls  are  strongly  and  char- 
acteristically thickened  and  pitted.  In  no  two  plants  are  they 
alike,  and  in  each  plant  they  are  important  diagnostic  characters. 

Storage  cell  walls  consist  of  reserve  cellulose,  a  form  of 
cellulose  which  is  rendered  soluble  by  ferments,  and  utilized 
as  food  during  the  growth  of  the  seed.  Reserve  cellulose  is 
hard,  bony,  and  of  a  waxy  lustre  when  dry.  Upon  boiling  in 
water  the  walls  swell  and  become  soft. 

The  structure  of  the  reserve  cellulose  varies  greatly  in  the 
different  seeds  in  which  it  occurs  in  the  thickness  of  the  walls 
and  in  the  number  and  Character  of  the  pores. 


PLATE  68 


RESERVE  CELLULOSE 

1.  Saw  palmetto  (Serenoa  serrulata,  [Michaux]  Hook.,  f.). 

2.  Areca  nut  (Areca  catechu,  L.). 

3.  Colchicum  seed  (Colchicum  autumnale,  L.). 
$-A.  Porous  side  wall. 

3-5.  Cell  cavity  above  the  side  wall. 


PLATE  69 


RESERVE  CELLULOSE 

1.  Endosperm  of  nux  vomica  (Strychnos  nux  vomica,  L.). 

2.  Endosperm  of  St.  Ignatia  bean  (Strychnos  ignatii,  Berg.). 


CHAPTER  IX 

CELL  CONTENTS 

The  cell  contents  of  the  plant  are  divided  into  two  groups: 
first,  organic  cell  contents;  and  secondly,  inorganic  cell  contents. 

The  organic  cell  contents  include  plastids,  starch  grains, 
mucilage,  inulin,  sugar,  hesperidin,  alkaloids,  glucocides,  tannin, 
resin,  and  oils. 

CHLOROPHYLL 

The  chloroplasts  of  the  higher  plants  are  green,  and  they 
vary  somewhat  in  size,  but  they  have  a  similar  structure  and 
form. 

Chloroplasts  are  mostly  oval  in  longitudinal  view  and  rounded 
in  cross-section  view.  Each  chlorophyll  grain  has  an  extremely 
thin  outer  wall,  which  encloses  the  protoplasmic  substance,  the 
green  granules,  a  green  pigment  (chlorophyll),  and  a  yellow 
pigment  (xanthophyll) .  Frequently  the  wall  includes  starch, 
oil  drops,  and  protein  crystals. 

Chloroplasts  are  arranged  either  in  a  regular  peripheral 
manner  along  the  walls,  or  they  are  diffused  throughout  the 
protoplast. 

The  palisade  cells  of  most  leaves  are  packed  with  chlorophyll 
grains.  In  the  mesophyll  cells  the  chlorophyll  grains  are  not 
so  numerous,  and  they  are  arranged  peripherally  around  the 
innermost  part  of  the  wall. 

Chloroplasts  multiply  by  fission — that  is,  each  chloroplast 
divides  into  two  equal  halves,  each  of  which  develops  into  a 
normal  chloroplast. 

Chlorophyll  occurs  in  the  palisade,  spongy  parenchyma,  and 
guard  cells  of  the  leaf;  in  the  collenchyma  and  parenchyma  of 
the  cortex  of  the  stems  of  herbs  and  of  young  woody  stems,  and, 
under  certain  conditions,  in  rhizomes  and  roots  exposed  to 
light.  Almost  without  exception  young  seeds  and  fruits  have 
chlorophyll. 

182 


CELL   CONTENTS  183 

In  powdered  leaves,  stems,  etc.,  the  chlorophyll  grains  occur 
in  the  cells  as  greenish,  more  or  less  structureless  masses.  Yet 
cells  with  chlorophyll  are  readily  distinguished  from  cells  with 
other  cell  contents.  In  witch-hazel  leaf  the  chlorophyll  grains 
appear  brownish  in  color.  Powdered  leaves  and  herbs  are 
readily  distinguished  from  bark,  wood,  root,  and  flower  powders. 

Leaves  and  the  stems  of  herbs  are  of  a  bright-green  color. 
With  the  exception  of  the  guard  cells,  the  chloroplasts  occur  one 
or  more  layers  below  the  epidermis;  but,  owing  to  the  trans- 
lucent nature  of  the  outer  walls  of  these  cells,  the  outer  cells  of 
leaves  and  stems  appear  green. 

Wild  cherry,  sweet  birch,  and,  in  fact,  most  trees  witn  smooth 
barks  have  chloroplasts  in  several  of  the  outer  layers  of  the 
cortical  parenchyma.  When  the  thin  outer  bark  is  removed 
from  these  plants,  the  underlying  layers  are  'seen  to  be  of  a 
bright-green  color. 

LEUCOPLASTIDS 

Leucoplastids,  or  colorless  plastids,  occur  in  the  underground 
portions  of  the  plant;  they  may,  when  these  organs  in  which 
they  occur  are  exposed  to  light,  change  to  chloroplastids. 

Leucoplasts  are  the  builders  of  starch  grains.  They  take 
the  chemical  substance  starch  and  build  or  mould  it  into  starch 
grains,  storage  starch,  or  reserve  starch. 

Other  characteristic  chromoplasts  found  in  plants  are  yellow 
and  red.  Yellow  chromoplasts  occur  in  carrot  root  and  nas- 
turtium flower  petals.  Red  plastids  occur  in  the  ripe  fruit  of 
capsicum. 

STARCH   GRAINS 

The  chemical  substance  starch  (C&HioOs)  is  formed  in  chloro- 
plasts. The  starch  thus  formed  is  removed  from  the  chloro- 
plasts to  other  parts  of  the  plant  because  it  is  the  function  of 
the  chloroplasts  to  manufacture  and  not  to  store  starch. 

The  starch  formed  by  the  chloroplasts  is  acted  upon  by  a 
ferment  which  adds  one  molecule  of  water  to  C6Hi0O5,  thus 
forming  sugar  C6Hi2O6.  This  sugar  is  readily  soluble  in  the 


184  HISTOLOGY   OF   MEDICINAL   PLANTS 

cell  sap,  and  is  conducted  to  all  parts  of  the  plant.  The  sugar 
not  utilized  in  cell  metabolism  is  stored  away  in  the  form  of 
reserve  starch  or  starch  grains  by  colorless  plastids  or  amyloplasts. 

The  amyloplasts  change  the  sugar  into  starch  by  extracting 
a  molecule  of  water.  This  structureless  material  (starch)  is 
then  formed  by  the  amyloplast  into  starch  grains  having  a 
definite  and  characteristic  form  and  structure." 

Starch  grams  vary  greatly  in  different  species  of  plants, 
owing  probably  to  the  variation  of  the  chemical  composition, 
density,  etc.,  of  the  protoplast,  and  to  the  environmental  con- 
ditions under  which  the  plant  is  growing. 

OCCURRENCE 

Starch  grains  are  simple,  compound,  or  aggregate.  Simple 
starch  grains  may  occur  as  isolated  grains  (Plates  70,  71,  and 
72),  or  they  may  be  associated  as  in  cardamon  seed,  white  pepper, 
cubeb,  and  grains  of  paradise,  where  the  simple  grains  stick 
together  in  masses,  having  the  outline  of  the  cells  in  which  they 
occur.  These  masses  are  known  as  aggregate  starch. 

Aggregate  starch  (Plate  76)  varies  greatly  in  size,  form,  and 
in  the  nature  of  the  starch  grains  forming  the  aggregations. 

Compound  starch  grains  may  be  composed  of  two  or  more 
parts,  and  they  are  designated  as  2,  3,  4,  5,  etc.,  compound 
(Plate  75). 

The  parts  of  a  compound  grain  may  be  of  equal  size  (Plate 
75,  Fig.  4),  or  they  may  be  of  unequal  size  (Plate  75,  Fig.  2). 

In  most  powders  large  numbers  of  the  parts  of  the  com- 
pound grains  become  separated.  The  part  in  contact  with  other 
grains  shows  plane  surfaces,  while  the  external  part  of  the  grain 
has  a  curved  surface.  There  will  be  one  plane  and  one  curved 
surface  if  the  grain  is  a  half  of  a  two-compound  grain;  two 
plane  and  one  curved  surface  if  the  grain  is  a  part  of  a  three- 
compound  grain,  etc. 

The  simple  starch  grains  forming  the  aggregations  become 
separated  during  the  milling  process  and  occur  singly,  so  that 
in  the  drugs  cited  above  the  starch  grains  are  solitary  and 
aggregate. 

Many  plants  contain  both  simple  and  compound  starch 
grains  (Plate  74,  Fig.  3). 


CELL   CONTENTS  185 

In  some  forms — e.g.,  belladonna  root  (Plate  75,  Fig.  2)  the 
compound  grains  are  more  numerous;  while  in  sanguinaria  the 
simple  grains  are  more  numerous,  etc. 

OUTLINE 

The  outline  of  starch  grains  is  made  up  of  (i)  rounded,  (2) 
angled,  and  (3)  rounded  and  angled  surfaces. 

Starch  grains  with  rounded  surfaces  may  be  either  spherical, 
as  in  Plate  74,  Fig.  3,  or  oblong  or  elongated,  as  in  Plate  71, 
Fig.  i. 

Other  starches  with  rounded  surfaces  are  shown  on  Plates 
72  and  73. 

Angled  outlined  grains  are  common  to  cardamon  seed,  white 
pepper,  cubebs,  grains  of  paradise  (Plate  76,  Fig.  4),  and  to  corn 
(Plate  70,  Fig.  3). 

The  outlines  of  all  compound  grains  are  made  up  partly  of 
plane  and  partly  of  curved  surfaces. 

SIZE 

The  size  (greatest  diameter)  of  starch  varies  greatly  even 
in  the  same  species,  but  for  each  plant  there  is  a  normal  variation. 

In  spherical  starch  grains  the  size  of  the  individual  grains  is 
invariable,  but  in  elongated  starch  grains  and  in  parts  of  com- 
pound grains  the  size  will  vary  according  to  the  part  of  the  grain 
measured.  In  zedoary  starch  (Plate  71,  Fig.  4),  for  instance, 
the  size  will  vary  according  to  whether  the  end,  side,  or  surface 
of  the  starch  grain  is  in  focus. 

The  parts  of  compound  grains  often  vary  greatly  in  size. 
Such  a  variation  is  shown  in  Plate  75,  Fig.  2. 

HILUM 

The  hilum  is  the  starting-point  of  the  starch  grain  or  the 
first  part  of  the  grain  laid  down  by  the  amyloplast.  The  hilum 
will  be  central  if  formed  in  the  middle  of  the  amyloplast,  and 
excentral  if  formed  near  the  surface  of  the  amyloplast.  It 
has  been  shown  that  the  developing  starch  grain  with  eccentric 
hilum  usually  extends  the  wall  of  the  amyloplast  if  it  does  not 
actually  break  through  the  wall.  Starch  grains  with  excentral 
hilums  are  therefore  longer  than  broad. 


PLATE   70 


STARCH 

1.  Calabar  bean  (Physostigma  venenosum,  Balfour). 

2.  Marshmallow  root  (Althaea  ojficinalis,  L.). 

3.  Field  corn  (Zea  mays,  L.). 


STARCH 

I.  Galanga  root  (Alpinia  officinarum,  Hance).  2.  Kola  nut  (Cola  vera, 
[K.]  Schum.).  3.  Geranium  rhizome  (Geranium  maculatum,  L.).  4.  Zedoary 
root  (Curcuma  zedoaria,  Rose.).  4~A.  Surface  view  of  starch  grain.  4-5.  Side 
view  of  starch  grain.  4-C.  End  view  of  starch  grain. 


188  HISTOLOGY    OF   MEDICINAL   PLANTS 

In  central  hilum  starch  grains  the  grain  is  laid  down  around 
the  hilum  in  the  form  of  concentric  layers.  Thes$  layers  are 
of  variable  density.  The  dense  layers  are  formed  when  plenty 
of  sugar  is  available,  and  the  less  dense  layers  are  formed  when 
little  sugar  is  available.  The  unequal  density  of  the  different 
layers  gives  the  striated  appearance  characteristic  of  so  many 
starch  grains. 

In  eccentric  hilum  starch  grains  the  starch  will  be  deposited 
in  layers  which  are  outside  of  and  successively  farther  from  the 
hilum. 

The  term  hilum  has  come  to  have  a  broader  meaning  than 
formerly.  Hilum  includes  at  the  present  time  not  only  the 
starting-point  of  the  starch  grain,  but  the  fissures  which  form 
in  the  grain  upon  drying.  In  all  cases  these  fissures  originate 
in  the  starting-point,  hilum,  and  in  some  cases  extend  for  some 
distance  from  it.  The  hilum,  when  excentral,  may  occur  in 
the  broad  end  of  the  grain,  galanga,  and  geranium  (Plate  71, 
Figs,  i  and  3),  or  in  the  narrow  end  of  the  grain,  zedoary  (Plate 
71,  Fig.  4). 

NATURE   OF   THE  HILUM 

The  hilum,  whether  central  or  excentral,  may  be  rounded 
(Plate  75,  Fig.  i);  or  simple  cleft,  which  may  be  straight  (Plate 
71,  Fig.  i);  or  curved  cleft  (Plate  71,  Fig.  2);  or  the  hilum  may 
be  a  multiple  cleft  (Plate  74,  Fig.  3). 

In  studying  starches  use  cold  water  as  the  mounting  medium, 
because  in  cold  water  the  form  and  structure  are  best  shown, 
and  because  there  is  no  chemical  action  on  the  starch.  On  the 
other  hand,  the  form  and  structure  will  vary  considerably  if 
the  starch  is  mounted  in  hot  water  or  in  solutions  of  alkalies 
or  acids.  The  hilum  appears  colorless  when  in  sharp  focus,  and 
black  when  out  of  focus. 

Starch  grains,  when  boiled  with  water,  swell  up  and  finally 
disintegrate  to  form  starch  paste. 

Starch  paste  turns  blue  upon  the  addition  of  a  few  drops  of 
weak  lugol  solution.  Upon  heating,  this  blue  solution  is  de- 
colorized, but  the  color  reappears  upon  cooling.  If  a  strong 
solution  of  lugol  is  used  in  testing,  the  color  will  be  bluish  black. 


PLATE  72 


STARCH 

1.  Orris  root  (Iris  florentinia  L.). 

2.  Stillingea  root  (Stillingea  sylvatica,  L.). 

3.  Calumba  root  (Jatcorhiza  palmata,  [Lam.]  Miers.). 


1 


PLATE   73 


STARCH 

1.  Male  fern  (Dryopteris  marginalis,  [L.]  A.  Gray), 

2.  African  ginger  (Zingiber  officinalis,  Rose.). 

3.  Yellow  dock  (Rumex  crispus,  L.). 

4.  Pleurisy  root  (Asclepias  tuberosa,  L.). 


PLATE  74 


STARCH 

1.  Kava-kava  (Piper  methysticum,  Forst.,  f.). 

2.  Pokeroot  (Phytolacca  americana,  L.). 

3.  Rhubarb  (Rheum  officinale,  Baill.). 


PLATE   75 


STARCH  GRAINS 

1.  Bryonia  (Bryonia  alba,  L.). 

2.  Belladonna  root  (Atropa  belladonna,  L.). 

3.  Valerian  root  (Valeriana  officinalis,  L.). 

4.  Colchicum  root  (Colchicum  autumnale,  L.). 


PLATE  76 


STARCH  MASSES 

1.  Aggregate  starch  of  cardamon  seed  (Elettaria  cardamomum,  Maton). 

2.  Aggregate  starch  of  white,  pepper  (Piper  nigrum,  L.). 

3.  Aggregate  starch  of  cubebs  (Piper  cubeba,  L:,  f.). 

4.  Aggregate  starch  of  grains  of  paradise  (Amomum  meleguetta,  Rose.). 


194  HISTOLOGY   OF  MEDICINAL  PLANTS 

INULIN 

Inulin  is  the  reserve  carbohydrate  material  found  in  the 
plants  of  the  composite  family. 

The  medicinal  plants  containing  inulin  are  dandelion,  chicory, 
elecampane,  pyrethrum,  and  burdock.  Plate  77,  Figs,  i  and  2 
show  masses  of  inulin  in  dandelion  and  pyrethrum. 

In  these  plants  the  inulin  occurs  in  the  form  of  irregular, 
structureless,  grayish- white  masses  (Plate  77).  In  powdered 
drugs  inulin  occurs  either  in  the  parenchyma  cell  or  as  irregular 
isolated  fragments  of  variable  size  and  form.  Inulin  is  structure- 
less and  the  inulin  from  one  plant  cannot  be  distinguished 
microscopically  from  the  inulin  of  another  plant.  For  this 
reason  inulin  has  little  or  no  diagnostic  value.  The  presence 
or  absence  of  inulin  should  always  be  noted,  however,  in  examin- 
ing powdered  drugs,  because  only  a  few  drugs  contain  inulin. 

When  cold  water  is  added  to  a  powder  containing  inulin  it 
dissolves.  Solution  will  take  place  more  quickly,  however,  in 
hot  water.  Inulin  occurs  in  the  living  plant  in  the  form  of  cell 
sap.  If  fresh  sections  of  the  plant  are  placed  in  alcohol  or 
glycerine,  the  inulin  precipitates  in  the  form  of  crystals. 

MUCILAGE 

Mucilage  is  of  common  occurrence  in  medicinal  plants. 
Characteristic  mucilage  cavities  filled  with  mucilage  occur  in 
sassafras  stem  (Plate  66,  Fig.  2),  in  elm  bark  (Plate  66,  Fig.  i), 
in  althea  root,  in  the  outer  layer  of  mustard  seed,  and  in  the 
stem  of  cactus  grandiflorus.  In  addition,  mucilage  is  found 
associated  with  raphides  in  the  crystal  cells  of  sarsaparilla, 
squill,  false  unicorn,  and  poly gona turn. 

When  drugs  containing  mucilage  are  added  to  alcohol, 
glycerine,  and  water  mixture,  the  mucilage  swells  slightly  and 
becomes  distinctly  striated,  but  it  will  not  dissolve  for  a  long 
tune.  Refer  to  Plate  79,  Fig.  6. 

Mucilage,  when  associated  with  raphides,  swells  and  rapidly 
dissolves  when  added  to  alcohol,  glycerine,  and  water  mixture. 
The  mucilage  is,  therefore,  different  from  the  mucilage  found 
in  mucilage  cavities,  because  it  is  more  readily  soluble. 

In   coarse-powdered   bark   and   other   mucilage   containing 


INULIN  (Inula  helenium,  L.) 

1.  Inulin  in  the  parenchyma  cells  of  dandelion  root. 

2.  Inulin  from  Roman  pyrethrum  root  (Anacyclus  pyrethrum,  [L.]  D.  C.). 


196  HISTOLOGY   OF   MEDICINAL   PLANTS 

drugs  the  mucilage  masses  are  mostly  spherical  or  oval  in  outline 
(Plate  66,  Figs.  2  and  3)  the  form  being  similar  to  the  cavity 
in  which  the  mass  occurs. 

Acacia,  tragacanth,  and  India  gum  consist  of  the  dried 
mucilaginous  excretions. 

HESPERIDIN 

Hesperidin  occurs  in  the  epidermal  cells  of  short  and  long 
buchu.  It  is  particularly  characteristic  in  the  epidermal  cells 
of  the  dried  leaves  of  short  buchu.  In  these  leaves  the  hesperidin 
occurs  in  masses  which  resemble  rosette  crystals  (Plate  54,  Fig.  i). 

Hesperidin  is  insoluble  in  glycerine,  alcohol,  and  water,  but 
it  dissolves  in  alkali  hydroxides,  forming  a  yellowish  solution. 

VOLATILE   OILS 

Volatile  oils  occur  in  cinnamon  stem  bark,  sassafras  root 
bark,  flowers  of  cloves,  and  in  the  fruits  of  allspice,  anise,  fennel, 
caraway,  coriander,  and  cumin. 

In  none  of  these  cases  is  the  volatile  oil  diagnostic,  but  its 
presence  must  always  be  determined. 

When  a  powdered  drug  containing  a  volatile  oil  is  placed 
in  alcohol,  glycerine,  and  water  mixture  the  volatile  oil  con- 
tained in  the  tissues  will  accumulate  at  the  broken  end  of  the 
cells  in  the  form  of  rounded  globules,  while  the  volatile  oil 
adhering  to  the  surface  of  the  fragments  will  dissolve  in  the 
mixture  and  float  in  the  solution  near  the  under  side  of  the 
cover  glass.  Volatile  oil  is  of  little  importance  in  histological 
work. 

TANNIN 

Tannin  masses  are  usually  red  or  reddish  brown.  Tannin 
occurs  in  cork  cells,  medullary  rays  of  white  pine  bark  (Plate  48, 
Fig.  B),  stone  cells,  and  in  special  tannin  sacs. 

The  stone  cells  of  hemlock  and  tamarac  bark  and  the  medul- 
lary rays  of  white  pine  and  hemlock  bark  contain  tannin. 

Tannin  associated  with  prisms  occurs  in  tannin  sacs  in  white 
pine  and  tamarac  bark.  These  sacs  are  frequently  several 
millimeters  in  length  and  contain  a  great  number  of  crystals 
surrounded  by  tannin. 


CELL   CONTENTS  197 

Deposits  of  tannin  are  colored  bluish  black  with  a  solution 
of  ferric  chloride. 

ALEURONE  GRAINS 

Aleurone  grains  are  small  granules  of  variable  structure, 
size,  and  form,  and  they  are  composed  of  reserve  proteins. 
They  occur  in  celery,  fennel,  coriander,  and  anise,  fruits,  in 
sesame,  sunflower,  curcas,  castor  oil,  croton  oil,  bitter  almond, 
and  other  oil  seeds. 

In  many  of  the  seeds  the  aleurone  grains  completely  fill  the 
cells  of  the  endosperm,  embryo,  and  peristerm.  In  wheat,  rye, 
barley,  oats,  and  corn  the  aleurone  grains  occur  only  in  the 
outer  layer  or  layers  of  the  endosperm,  the  remaining  layers 
in  these  cases  being  filled  with  starch. 

In  powdered  drugs  the  aleurone  grains  occur  in  parenchyma 
cells  or  free  in  the  field. 

STRUCTURE  OF  ALEURONE   GRAINS 

Aleurone  grains  are  very  variable  in  structure.  The  simplest 
grains  consist  of  an  undifferentiated  mass  of  proteid  substance 
surrounded  by  a  thin  outer  membrane.  In  other  grains  the 
proteid  substance  encloses  one  or  more  rounded  denser  proteid 
bodies  known  as  globoids.  In  other  grains  a  crystalloid — crystal- 
like  proteid  substance — is  present  in  addition  to  the  globoid. 
In  some  grains  are  crystals  of  calcium  oxalate,  which  may  occur 
as  prisms  or  as  rosettes.  All  the  different  parts,  however,  do 
not  occur  in  any  one  grain.  In  castor-oil  seed  (Plate  770,  Fig.  8) 
are  shown  the  membrane  (A),  the  ground  mass  (J3),  the  crys- 
talloid (C),  and  the  globoid  (D). 

FORM  OF  ALEURONE  GRAINS 

Much  attention  has  been  given  to  the  study  of  the  special 
parts  of  the  aleurone  grains,  but  one  of  the  most  important 
diagnostic  characters  has  been  overlooked,  namely,  that  of 
comparative  form.  For  the  purposes  of  comparing  the  forms  of 
different  grains,  they  should  be  mounted  in  a  medium  in  which 
the  grain  and  its  various  parts  are  insoluble.  Oil  of  'cedar  is 
such  a  medium.  The  variation  in  form  and  size  of  the  aleurone 
grains  when  mounted  in  oil  of  cedar  is  shown  in  Plate  770. 


198  HISTOLOGY  OF  MEDICINAL  PLANTS 

DESCRIPTION  OF  ALEURONE  GRAINS 

The  aleurone  grains  of  curcas  (Plate  770,  Fig.  i)  vary  in  form 
from  circular  to  lens-shaped,  and  each  grain  contains  one  or 
more  globoids.  The  globoids  are  larger  when  they  occur  singly. 
In  sunflower  seed  (Plate  770,  Fig.  2)  the  grains  vary  from  reni- 
form  to  oval,  and  one  or  more  globoids  are  present;  many  occur 
in  the  center  of  the  grain. 

The  aleurone  grains  of  flaxseed  (Plate  770,  Fig.  3)  resemble 
in  form  those  of  sunflower  seed,  but  the  grains  are  uniformly 
larger  and  some  of  the  grains  contain  as  many  as  five 
globoids. 

In  bitter  almond  (Plate  770,  Fig.  4)  the  aleurone  grains  are 
mostly  circular,  but  a  few  are  nearly  lens-shaped.  A  few  of 
the  large,  rounded  grains  contain  as  many  as  nine  globoids; 
in  such  cases  one  of  the  globoids  is  likely  to  be  larger  than  the 
others.  The  aleurone  grains  of  cro ton-oil  seed  (Plate  770,  Fig.  5) 
are  circular  in  outline,  variable  in  form,  and  each  grain  contains 
from  one  to  seven  globoids. 

In  sesame  seed  (Plate  770,  Fig.  6)  the  typical  grain  is  angled 
in  outline  and  the  large  globoid  occurs  in  the  narrow  or  con- 
stricted end. 

The  aleurone  grains  of  castor-oil  seed  (Plate  770,  Fig.  7)  re- 
semble those  of  sesame  seed,  but  they  are  much  larger,  and 
many  of  the  grains  contain  three  large  globoids.  When  these 
grains  are  mounted  in  sodium-phosphate  solution,  the  crystal- 
loid becomes  visible. 

TESTS  FOR  ALEURONE  GRAINS 

Aleurone  grains  are  colored  yellow  with  nitric  acid  and  red 
with  Millon's  reagent. 

The  proteid  substance  of  the  mass  of  the  grain,  of  the  globoid, 
and  of  the  crystalloid,  reacts  differently  with  different  reagents 
and  dyes. 

The  ground  substance  and  the  crystalloids  are  soluble  in 
dilute  alkali,  while  the  globoids  are  insoluble  in  dilute  alkali. 

The  ground  substance  and  crystalloids  are  soluble  in  sodium 
phosphate,  while  the  globoids  are  insoluble  in  sodium  phosphate. 

Calcium  oxalate  is  insoluble  in  alkali  and  acetic  acid,  but 
it  dissolves  in  hydrochloric  acid. 


PLATE 


6 


ALEURONE  GRAINS 

1.  Curcas  (Jatropha  curcas,  L.). 

2.  Sunflower  seed  (Helianthus  annuus,  L.). 

3.  Flaxseed  (Linum  usitatissimum,  L.). 

4.  Bitter  almond  (Prunus  amygdalus,  amara,  D.C.). 

5.  Croton-oil  seed  (Croton  tiglium,  L.). 

6.  Sesame  seed  (Sesamum  indicum,  L.). 

7  and  8.  Castor-oil  seed  (Ricinus  communis,  L.). 


200  HISTOLOGY    OF   MEDICINAL   PLANTS 

CRYSTALS 

Calcium  oxalate  crystals  form  one  of  the  most  important 
inorganic  cell  contents  found  in  plants,  because  of  the  per- 
manency of  the  crystals,  and  because  the  forms  common  to 
a  given  species  are  invariable.  By  means  of  calcium  oxalate 
crystals  it  is  possible  to  distinguish  between  different  species. 
In  butternut  root  bark,  for  instance,  only  rosette  crystals  are 
found,  while  in  black  walnut  root  bark — a  common  substitute 
for  -butternut  bark — both  prisms  and  rosettes  occur.  This  is 
only  one  of  the  many  examples  which  could  be  cited. 

These  crystals,  for  purposes  of  study,  will  be  grouped  into 
four  principal  classes,  depending  upon  form  and  not  upon  crystal 
system.  These  classes  are  micro-crystals,  raphides,  rosettes, 
and  solitary  crystals. 

MICRO-CRYSTALS 

Micro-crystals  are  the  smallest  of  all  the  crystals.  Under  the 
high  power  of  the  microscope  they  appear  as  a  V,  a  Y,  an  X, 
and  as  a  T.  They  are,  therefore,  three-  or  four- angled  (Plate  78). 
The  thicker  portions  of  these  crystals  are  the  parts  usually 
seen,  but  when  a  close  observation  of  the  crystals  is  made  the 
thin  portions  of  the  crystal  connecting  the  thicker  parts  may 
also  be  observed.  Micro-crystals  should  be  studied  with  the 
diaphragm  of  the  microscope  nearly  closed  and  with  the  high- 
power  objective  in  position.  While  observing  the  micro-crystals, 
raise  and  lower  the  objective  by  the  fine  adjustment  in  order  to 
bring  out  the  structure  of  the  crystal  more  clearly.  Micro- 
crystals  occur  in  parenchyma  cells  of  belladonna,  scopola, 
stramonium,  and  bittersweet  leaves;  in  belladonna,  in  horse- 
nettle  root,  in  scopola  rhizome,  in  bittersweet  stems,  and  in 
yellow  and  red  cinchona  bark,  etc. 

The  crystals  in  each  of  the  above  parts  of  the  plant  are  similar 
in  form,  the  only  observed  variation  being  that  of  size.  Their 
presence  or  absence  should  always  be  noted  when  studying 
powders. 

RAPHIDES 

Raphides,  which  are  usually  seen  in  longitudinal  view,  re- 
semble double-pointed  needles.  They  are  circular  in  cross- 


PLATE   78 


3 


& 


MICRO-CRYSTALS 

1.  Horse-nettle  root  (Solatium  carolinense,  L.). 

2.  Scopola  rhizome  (Scopola  carniolica,  Jacq.). 

3.  Belladonna  root  (Atropa  belladonna,  L.)- 

4.  Bittersweet  stem  (Solanum  dulcamara,  L.). 

5.  Scopola  leaf  (Scopola  carniolica,  Jacq.). 

6.  Tobacco  leaf  (Nicotiana  tabacum,  L.). 

7.  Belladonna  leaf  (Atropa  belladonna,  L.). 


202  HISTOLOGY  OF  MEDICINAL  PLANTS 

section,  and  the  largest  diametej  is  at  the  centre,  from  which 
they  taper  gradually  toward  either  end  to  a  sharp  point. 

Raphides  occur  in  bundles,  as  in  false  unicorn  root  (Plate  79, 
Figs.  6,  A,  B,  and  C),  rarely  as  solitary  crystals. 

In  ipecac  root  the  crystals  are  usually  solitary.  In  sar- 
saparilla  root,  squill,  etc.,  the  raphides  occur  both  in  clusters, 
part  of  bundle,  or  in  bundles,  and  as  solitary  crystals. 

In  most  drugs  the  crystals  are  entire;  but  in  squills,  where 
the  raphides  are  very  large,  they  are  broken.  In  phytolacca 
(Plate  79,  Fig.  i)  and  in  hydrangea,  the  raphides  are  usually 
broken,  owing  to  the  fact  that  these  drugs  contain  large  quan- 
tities of  fibres  which  break  them  up  into  fragments  when  the 
drug  is  milled. 

There  is  the  greatest  possible  variation  in  the  size  of  raphides 
in  the  same  and  in  different  drugs,  but  the  larger  forms  are 
constant  in  the  same  species. 

Raphides  are  deposited  in  parenchyma  cells  and  in  special 
raphides  sacs.  These  crystals  are  always  surrounded  with 
mucilage. 

ROSETTE  CRYSTALS 

Rosette  crystals  are  compound  crystals  composed  of  an 
aggregation  of  small  crystals  arranged  in  a  radiating  manner 
around  a  central  core.  This  core  appears  nearly  black,  and 
the  whole  mass  is  nearly  spherical.  The  free  ends  of  the  crystals 
are  sharp-pointed  or  blunt. 

Characteristic  rosette  crystals  occur  in  frangula  bark,  spike- 
nard root,  wahoo  stem,  root  bark,  rhubarb,  etc.  (Plate  80, 
Figs',  i,  2,  3,  4,  5,  and  6). 

These  crystals  are  very  variable  in  size.  This  variation  is 
illustrated  by  the  crystals  of  Plate  80. 

Usually  there  is  a  variation  in  size  of  the  crystals  occurring 
in  a  given  plant,  but  for  each  plant  there  is  a  more  or  less  uni- 
form variation.  For  instance,  the  largest  rosette  crystal  occur- 
ring in  wahoo  root  bark  (Plate  80,  Fig.  5)  is  smaller  than  the 
largest  crystal  occurring  in  rhubarb  (Plate  80,  Fig.  6),  etc. 

The  prisms  forming  the  rosette  crystals,  like  all  prisms, 
decompose  white  light,  with  the  result  that  rosette  crystals 
frequently  appear  variously  colored.  Rhubarb  crystals,  for 


PLATE   79 


RAPHIDES 

i.  Phytolacca  root  (Phytolacca  americana,  L.).  2.  Squills  (Urginea  mari- 
time, [L.]  Baker).  3.  Hydrangea  root  (Hydrangea  arborescens,  L.).  4.  Con- 
vallaria  (Convallaria  majalis,  L.).  5.  Carthagean  ipecac  (Cephcdis  acuminata 
Karst.)  6.  Bundle  of  raphides  from  false  unicorn  root. 

A.  Bundle  surrounded  with  mucilage.  B.  Mucilage  expanded  and  par- 
tially dissolved.  C.  Bundle  free  of  mucilage. 


PLATE   80 


6 


ROSETTE  CRYSTALS 

1.  Frangula  bark  (Rhamnus  frangula,  L.). 

2.  White  oak  bark  (Quercus  alba,  L.). 

3.  Spikenard  root  (Aralia  racemosa,  L.). 

4.  Wahoo  stem  bark  (Euonymus  atropurpureus,  Jacq.). 

5.  Wahoo  root  bark  (Euonymus  atropurpureus,  Jacq.). 

6.  Rhubarb  (Rheum  ojficinale,  Baill.). 


CELL  CONTENTS  205 

instance,  are  blue  or  violet.     Most  of  the  smaller  rosette  crystals, 
however,  appear  grayish  white  with  a  darker-colored  centre. 

Rosette  crystals  occur  in  parenchyma  cells  (Plate  81,  Fig.  4) 
and  in  medullary  rays  (Plate  81,  Fig.  3). 

SOLITARY  CRYSTALS 

Solitary  crystals  are  the  most  variable  of  all  the  forms  of 
calcium  oxalate.  They  usually  occur  in  crystal  cells  associated 
with  bast  fibres  and  stone  cells,  less  frequently  in  stone  cells 
(Plate  33,  Fig.  2).  There  are  many  different  and  characteristic 
forms  of  prisms.  The  more  common  are:  t 

1.  Rectangular: 

A.  Parallelepipeds. 

B.  Cubes. 

2.  Polyhedrons: 

A.  Irregular  polyhedrons. 

I.  Flat  bases. 

(a)  NoH-notched. 

(b)  Notched. 
II.  Tapering  bases. 

B.  Octohedrons. 

The  crystals  occurring  in  Batavia  cinnamon  and  henbane 
leaves  are  parallelepipeds  (Plate  82,  Figs,  i  and  2).  . 

The  crystals  occurring  in  cactus  grandiflorus,  hemlock  bark, 
krameria  root,  and  soap  bark  are  irregular  polyhedrons  (Plate 
83).  They  are  longer  than  broad,  and  the  ends  are  tapering. 
The  crystal  of  cactus  grandiflorus  has  the  narrowest  diameter 
of  these  four,  while  the  crystals  of  soap  bark  have  the  widest 
diameter.  In  coca  leaf,  xanthoxylum  bark,  elm  bark,  Spanish 
licorice,  and  in  white  oak  (Plate  84),  and  in  cocillina  bark  (Plate 
82,  Fig.  4)  the  crystals  are  all  irregular  polyhedrons  with  flat 
bases.  They  are  mostly  longer  than  broad  and  they  are  all 
widest  in  the  centre;  in  each  a  few  crystals  are  notched,  but 
most  of  the  crystals  are  not  notched. 

The  crystals  in  quassia  wood,  uva-ursi  leaf,  and  most  of  those 
of  quebracho  and  wild  cherry  bark  (Plate  86,  Figs,  i,  2,  3,  and  4) 
are  irregular  polyhedrons  with  flat  ends.  They  are  longer  than 
broad,  widest  at  the  centre,  and  non-notched. 

Cubes  occur  in  senna,  cascara  sagrada,  frangula,  white  pine, 


PLATE   81 


INCLOSED  ROSETTE  CRYSTALS 

1.  Hops  (Humulus  lupulus,  L.). 

2.  Bracts  of  cannabis  indica  (Cannabis  saliva,  variety  Indica,  Lamarck). 

3.  Medullary  rays  of  canella  alba. 

4.  Parenchyma  cells  of  mandrake  (Podophyllum  peltatum,  L.). 


PLATE  82 


SOLITARY  CRYSTAL 

1.  Batavia  cinnamon  (cinnamomum  burmanni,  Nees). 

2.  Henbane  leaves  (Hyoscyamus  niger,  L.). 

3.  Morea  nutgalls. 

4.  Cocillana  bark  (Guarea  rusbyi  [Britton],  Rusby). 


PLATE  83 


SOLITARY  CRYSTALS 

1.  Cactus  grandiflorus  (Cerdus  grandiflorus  [L.],  Britton  and  Rose). 

2.  Hemlock  bark  (Tsuga  canadensis  [L.],  Carr.). 

3.  Krameria  root  (Krameria  triandra,  Ruiz  and  Pav.). 

4.  Soapbark  (Quittaja  saponaria,  Molina). 


PLATE   84 


SOLITARY  CRYSTALS 

1.  Coca  leaf  (Erythroxylon  coca,  Lamarck). 

2.  Xanthoxylum  bark  (Zanthoxylum  americanum,  Miller). 

3.  Elm  bark  (Ulmus  fulva,  Michaux). 

4.  Spanish  licorice  root  (Glycyrrhiza  glabra,  L.). 

5.  White  oak  bark  (Quercus  alba,  L.). 


210  HISTOLOGY   OF   MEDICINAL  PLANTS 

tamarac  (Plate  85),  quassia,  uva-ursi,  quebracho,  and  in  wild 
cherry  (Plate  86). 

The  crystals  of  morea  nutgalls  (Plate  82,  Fig.  3)  are  octo- 
hedrons,  and  they  resemble  the  crystals  of  calcium  oxalate  found 
in  urinary  sediments. 

While  studying  the  prisms,  focus  first  on  the  upper  surface 
and  then  down  to  the  under  surface  in  order  to  observe  the 
forms  accurately. 

There  are  several  plants  in  which  more  than  one  form  of 
crystal  occur.  Rosette  crystals  and  prisms  are  associated,  for 
instance,  in  cascara  sagrada,  frangula,  condurango,  dogwood, 
and  pleurisy  root  (Plate  87,  Figs,  i,  2,  3,  4,  and  5). 

An  important  factor  to  be  kept  in  mind  in  studying  crystals 
is  the  number — whether  abundant,  as  in  rhubarb,  or  sparingly 
present,  as  in  mandrake,  etc.  Variation  in  the  number  of 
crystals  is  not  uncommon,  even  in  different  parts  of  the  same 
plants.  In  wahoo  stem  bark,  for  instance,  there  are  several 
times  as  many  rosette  crystals  as  there  are  in  the  root  bark. 

Crystals  of  calcium  oxalate  are  freely  soluble  in  dilute 
hydrochloric  acid  without  effervescence;  but  they  are  insoluble 
in  acetic  acid  and  in  sodium  and  potassium  hydroxide  solutions. 
With  sulphuric  acid  they  form  crystals  of  calcium  sulphate. 

CYSTOLITHS 

Cystoliths  consist  of  calcium  carbonate  deposited  over  and 
around  a  framework  of  cellulose. 

FORMS   OF  CYSTOLITHS 

The  forms  of  cystoliths  differ  greatly  in  the  different  plants 
in  which  they  occur. 

In  the  rubber-plant  leaf,  the  cystolith  resembles  a  bunch  of 
grapes  and  is  stalked;  in  ruellia  root  (Plate  87,  Fig.  i)  the  cysto- 
liths vary  from  nearly  circular  to  narrowly  cylindrical,  and  no 
stalk  is  present;  also  the  cystolith  nearly  fills  the  cell  in  which 
it  occurs.  In  the  hair  of  cannabis  indica  (Plate  88,  Fig.  3),  the 
cystolith  varies  in  form  according  to  the  size  and  shape  of  the 
hair,  but  in  all  the  hairs  the  cystolith  appears  to  be  attached  to 
the  upper  curved  part  of  the  inner  wall  of  the  hair. 


PLATE   85 


0 


SOLITARY  CRYSTALS 

1.  India  senna  (Cassia  angustifolia,  Vahl.). 

2.  Cascara  sagrada  bark  (Rhamnus  purshiana,  D.  C.). 

3.  Frangula  bark  (Rhamnus  frangula,  L.). 

4.  White  pine  bark  (Pinus  strobus,  L.). 

5.  Tamarac  bark  (Larix  laricina  [Du  Roi],  Koch). 


PLATE  86 


SOLITARY  CRYSTALS 

1.  Quassia  (Picrana  excelsa  [Swartz.],  Lindl.). 

2.  Uva-ursi  leaf  (Arctostaphylos  uva-ursi  [L.],  Spring.). 

3.  Quebracho  bark  (Aspidosperma  quebracho-bianco,  Schlechtendal). 

4.  Wild-cherry  bark  (Prunus  serotina,  Ehrh.). 


PLATE   87 


ROSETTE  CRYSTALS  AND  SOLITARY  CRYSTALS  OCCURRING  IN 

1.  Cascara  sagrada  bark  (Rhamnus  purshiana,  D.C.). 

2.  Frangula  bark  (Rhamnus  frangula,  L.). 

3.  Cundurango  bark  (Marsdenia  cundurango,  [Triana]  Nichols). 

4.  Dogwood  root  bark  (Cornus  florida,  L.). 

5.  Pleurisy  root  (Asdepias  tuberosa,  L.). 


PLATE  88 


CYSTOLITHS 
ciliosa,  Pursl 

3.   Tarmabis  indica  (Cannabis  saliva,  variety  Indica,  Lam.) 


1.  Ruellia  root  (Ruellia  ciliosa,  Pursh.). 

2.  Pellionia  leaf. 


CELL   CONTENTS  215 

Cystoliths  occur,  then,  in  special  cavities,  in  parenchyma 
cells  (rubber-plant  leaf,  fig,  pellionea,  and  mulberry),  and  in 
non-glandular  hairs  (cannabis  indica). 

In  powdered  ruellia  root  the  cystoliths  occur  in  or  are  sepa- 
rated from  the  parenchyma  cells. 

TESTS   FOR  CYSTOLITHS 

When  dilute  hydrochloric  acid  or  acetic  acid  is  added  to 
cystoliths  a  brisk  effervescence  takes  place  with  the  evolution 
of  carbon  dioxide  gas. 


Part  III 

HISTOLOGY  OF  ROOTS,  RHIZOMES,  STEMS, 

BARKS,   WOODS,   FLOWERS,   FRUITS, 

AND    SEEDS 

In  Part  II  the  different  types  of  cells  and  cell  contents  found 
in  plants  have  been  studied.  In  Part  III  it  will  be  shown  how 
these  different  cells  are  associated  and  the  nature  of  the  cell 
contents  in  the  different  parts  of  the  plant.  These  parts  are 
the  root,  the  rhizome,  the  stem  of  herbs,  bark  and  wood  of 
woody  stems,  the  leaf,  the  flower,  the  fruit,  and  the  seed. 


CHAPTER  I 

ROOTS  AND   RHIZOMES 

Some  fifty-five  roots,  rhizomes,  and  rhizomes  and  roots  are 
official  in  the  pharmacopoeia  and  national  formulary.  About 
5  of  these  are  obtained  from  monocotyledonous  plants,  and 
50  from  dicotyledonous  plants. 

In  studying  the  structure  of  roots  and  rhizomes,  then,  it 
must  first  be  determined  whether  the  root  in  question  is  mono- 
cotyledonous or  dicotyledonous.  This  fact  is  ascertained  by 
determining  the  type  of  the  fibro- vascular  bundle.  The  bundle 
is  of  the  open  collateral  type  in  all  rhizomes  and  roots  obtained 
from  monocotyledonous  plants,  but  it  is  closed,  radial,  or  con- 
centric in  the  monocotyledonous  type. 

In  both  of  these  groups  the  cellular  plan  of  structure  is 
similar,  the  chief  variation  being  the  absence  of  one  or  more 
types  of  cells,  the  variation  in  the  amount,,  in  arrangement,  in 
the  anatomical  structure,  in  the  color,  and  in  the  cell  contents 
of  the  individual  cells.  These  facts  will  be  impressed  on  the 
mind  while  studying  the  rhizomes  and  the  roots. 

CROSS-SECTION   PINK  ROOT 

The  cross-section  of  pink  root  (Plate  89)  has  the  following 
structure : 

Epidermis.  The  epidermal  cells  are  small,  nearly  as  long 
as  broad,  and  the  outer  wall  is  thicker  and  darker  in  color  than 
the  side  and  inner  walls.  The  cells  usually  contain  air. 

Cortex.  The  cortical  parenchyma  cells  are  very  large  and 
somewhat  rounded  in  outline,  and  the  walls  are  white.  There 
are  about  twelve  rows  of  these  cells,  and  each  cell  contains 
numerous  small,  rounded  starch  grains. 

Endodermis.  The  endodermal  cells  are  tangentially  elon- 
gated, and  the  walls  are  very  thin  and  white.  There  are  two 
or  three  layers  of  endodermal  cells;  the  cells'  outer  layers  are 
larger  than  the  cells  of  the  inner  layers. 

219 


PLATE  89 


CROSS-SECTION  OF  ROOT  OF  SPIGELIA  MARYLANDICA,  L. 
i.  Epidermis.     2.  Cortical  parenchyma.     2'.  Intercellular  space, 
dodermis.     4.  Pericycle.     5.  Cambium.     6.  Xylem.     7.  Pith. 


3.  En- 


ROOTS  AND  RHIZOMES  221 

Pericycle.  The  cells  forming  the  pericycle  are  sieve  cells 
and  phloem  parenchyma.  The  sieve  cells  are  small,  angled  cells 
with  extremely  thin,  white  walls. 

The  phloem  parenchyma  resemble  the  sieve  cells,  except 
that  they  are  larger. 

Cambium.  The  cambium  cells  are  rectangular  in  shape; 
the  walls  are  thin  and  white. 

Xylem.  The  xylem  is  composed  of  tracheids,  wood  paren- 
chyma, and  wood  fibres. 

Tracheids.  The  tracheids  are  the  largest  diameter  cells  of 
the  centre  of  the  root.  The  walls  are  thick  and  the  cells  are 
slightly  angled  in  outline. 

Wood  Parenchyma.  The  wood  parenchyma  cells  surrounding 
the  tracheids  are  five  to  seven,  angled,  and  the  walls  are  not 
so  thick  as  the  walls  of  the  tracheids. 

Medullary  Rays.  The  medullary  ray  cells  resemble  the 
structure  of  the  wood  parenchyma  cells,  but  they  are  radially 
elongated. 

Pith  Parenchyma.  The  cells  forming  the  pith  parenchyma 
are  larger  than  the  cells  of  wood  parenchyma,  but  their  struc- 
ture is  similar. 

CROSS-SECTION  RUELLIA  ROOT 

The  cross-section  of  ruellia  root  (Plate  90)  shows  the  follow- 
ing structure.  It  should  be  carefully  noted  how  the  structure 
differs  from  that  of  pink  root: 

Epidermis.  The  epidermal  cells  are  angled  and' variable  in 
size;  many  of  the  epidermal  cells  are  modified  as  root  hairs. 

Hypodermis.  The  cells  of  the  hypodermis  are  one  layer 
in  thickness  and  their  structure  is  similar  to  the  epidermal 
cells. 

Cortex.  The  cortex  contains  parenchyma  and  stone  cells. 
The  outer  layers  of  the  cortical  parenchyma  cells  are  round  in 
outline,  and  they  contain  dark-brown  cell  contents,  while  the 
cortical  parenchyma  cells  bordering  on  the  endodermis  are  small 
and  they  are  free  of  dark-brown  contents. 

Many  of  the  inner  parenchyma  cells  contain  amorphous 
deposits  of  calcium  carbonate. 


PLATE  90 


RUELLIA  ROOT  (Ruellia  ciliosa,  Pursh.). 

I.  Epidermis  with  root  hair.  2.  Parenchyma  cells  with  dark  content-. 
3.  Sclerid.  4.  Parenchyma  without  dark  cell  contents.  5.  Endodermis. 
6.  Bast  fibers  and  phloem.  7.  Cam!. him.  8.  Xylem.  10.  Pith. 


ROOTS   AND   RHJZOMKS  223 

The  stone  cells  are  porous  and  striated,  and  the  walls  are 
thick  and  white. 

Endodermis.  The  endodermal  cells  are  tangentially  elon- 
gated, and  the  walls  are  thin  and  white. 

Pericycle.  The  cells  forming  the  pericycle  are  the  sieve 
cells,  bast  fibres,  and  phloem  parenchyma. 

The  sieve  cells  are  small,  angled  cells  with  thin,  white  walls. 

The  phloem  parenchyma  cells  resemble  the  sieve  cells,  but 
they  are  larger. 

The  bast  fibres  occur  singly  or  in  groups  of  two  or  three. 
They  are  rounded  in  outline,  and  the  walls  are  white,  non- 
porous,  and  non-striated. 

Xylem.  The  xylem  is  composed  of  vessels,  wood  parenchyma, 
and  wood  fibres. 

Vessels.  The  vessels  are  rounded  in  outline  and  few  in 
munber. 

Wood  Parenchyma.  The  wood  parenchyma  cells  are  variable 
in  size  and  shape,  but  all  the  cells  are  angled  in  outline. 

Medullary  Rays.  The  medullary  ray  cells  are  not  clearly 
distinguishable. 

Pith  Parenchyma.  The  pith  parenchyma  cells  of  the  centre 
of  the  root  resemble  the  cortical  parenchyma  cells. 

That  the  structure  of  rhizomes  is  similar  to  the  structure  of 
roots  is  shown  by  the  drawings  of  spigelia  rhizome  (Plate  91), 
and  by  ruellia  rhizome  (Plate  92). 

CROSS- SECTION   SPIGELIA   RHIZOME 

The  cross-section  of  spigelia  rhizome  (Plate  91)  is  as  follows: 

Epidermis.  The  epidermal  cells  are  nearly  angled  and  free 
of  cell  contents. 

Cortex.  The  cortical  parenchyma  cells  are  usually  slightly 
tangentially  elongated.  The  cells  of  the  outer  layers  are  larger 
than  the  cells  of  the  inner  layers. 

Phloem.  The  phloem  contains  sieve  cells  and  phloem 
parenchyma.  The  sieve  cells  are  small,  angled  cells  with  thin, 
white  walls. 

The  phloem  parenchyma  cells  resemble  the  sieve  cells,  but 
they  are  larger. 

Cambium.     The  cambium  cells  are  rectangular,  and  they  are 


PLATE  91 


CROSS-SECTION  OF  RHIZOME  OF  SPIGELIA  MARYLANDICA,  L. 

I.  Epidermis.       2.  Cortical  parenchyma.       3.  Phloem.       4.  Cambium. 

5.  Xylem.       6.  Internal  phloem.       7.  Pith  with  starch. 


PLATE  92 


8 


CROSS-SECTION  OF  RHIZOME  OF  RUELLIA  CILIOSA,  Pursh. 
I.  Epidermis.       2.  Cystolith.       3.  Stone  cell.       4.  Cortical  parenchyma. 
5.  Bast  fibres.       6.  Pericycle.       7.  Xylem.       8.  Pith. 


226  HISTOLOGY   OF   MEDICINAL   PLANTS 

usually  not  clearly  seen  because  the  walls  are  partially 
collapsed. 

Xylem.  The  xylem  is  composed  of  vessels,  wood  parenchyma, 
medullary  rays,  and  pith  parenchyma. 

Vessels.  The  vessels  are  slightly  angled  in  outline  and  few 
in  number. 

Wood  Parenchyma.  The  wood  parenchyma  cells  are  small 
and  angled. 

Medullary  Rays.  The  medullary  ray  cells  are  tangentially 
elongated,  but  in  structure  resemble  the  wood  parenchyma  cells. 

Pith  Parenchyma.  The  pith  parenchyma  cells  are  rounded 
in  outline  and  contain  small,  simple,  rounded  starch  grains. 

CROSS-SECTION  RUELLIA  RHIZOME 

The  cross-section  of  ruellia  rhizome  (Plate  92)  differs  from 
the  structure  of  spigelia  rhizome,  It  is  as  follows: 

Epidermis.  The  epidermal  cells  vary  in  shape  from  nearly 
square  to  oblong,  and  they  are  rilled  with  dark-brown  cell 
contents. 

Cortex.     The  cortex  contains  parenchyma  and  stone  cells. 

The  outer  layer  of  the  cortical  parenchyma  cells  are  variable 
in  size  and  many  of  the  cells  contain  deposits  of  calcium  car- 
bonate and  dark  cell  contents;  the  inner  parenchyma  cells  are 
larger  and  they  are  free  of  the  dark-brown  cell  contents,  but 
many  of  the  cells  contain  deposits  of  calcium  carbonate. 

Stone  cells  with  thick,  white,  porous,  and  striated  walls  occur 
in  among  the  cortical  parenchyma  cells. 

Phloem.  The  phloem  contains  sieve  cells,  phloem,  paren- 
chyma, and  bast  fibres. 

The  sieve  cells  are  small  and  with  thin,  white,  angled  walls. 

The  phloem  parenchyma  cells  resemble  the  sieve  cells,  but 
they  are  larger. 

The  bast  fibres  occur  singly  or  in  groups  of  two  or  three. 
The  walls  are  white,  non-porous,  and  non-striated. 

Cambium.  The  cambium  layer  is  composed  of  rectangularly 
shaped  cells,  which  are  frequently  obliterated. 

Xylem.  The  xylem  contains  vessels,  wood  parenchyma, 
and  medullary  rays. 

The  vessels  are  large,  rounded  cells  with  thick  walls. 


ROOTS   AND   RHIZOMES  227 

The  wood  parenchyma  consists  of  thick- walled  cells  of  irreg- 
ular size  and  form. 

The  medullary  rays  are  tangentially  elongated  and  rectangular 
in  form. 

Pith  parenchyma.  The  pith  parenchyma  cells  are  rounded 
in  outline  and  as  large  as  the  cortical  parenchyma  cells. 

POWDERED   PINK  ROOT 

When  the  roots  and  rhizomes  of  spigelia  are  powdered  (Plate 
93)  they  show  the  following  structure: 

The  epidermal  cells  are  small  and  brownish  on  surface  view, 
varying  in  size  from  13  by  18  micromillimeters  to  31  by  40 
micromillimeters.  When  associated  with  parenchyma  they  ap- 
pear as  black  masses.  The  cortical  parenchyma  cells  are  rounded 
and  vary  in  size  from  23  by  26  micromillimeters  to  37.5  by  90 
micromillimeters.  Many  of  the  cells  from  the  foot  contain 
larger  quantities  of  minute  single  rounded  starch  grains  varying 
in  size  from  i  micromillimeter  to  4  micromillimeters.  The 
larger  round  single  starch  grains  are  found  in  both  the  cortical 
and  pith  parenchyma  of  the  rhizome.  They  vary  in  size  from 
5  micromillimeters  to  18  micromillimeters.  The  conducting 
elements  are  pitted  tracheids  varying  from  10  micromillimeters 
to  38  micromillimeters  in  diameter.  A  few  pitted  and  annular 
vessels  are  also  found.  The  only  fibres  occurring  are  found  in 
the  xylem.  They  are  not  a  prominent  feature  of  the  powder, 
as  their  walls  break  up  into  minute  fragments.  The  pith 
parenchyma  varies  in  size  from  13  by  19  micromillimeters  to 
75  by  82.5  micromillimeters.  It  is  in  these  cells  that  the  largest 
starch  grains  occur. 

Distinguishing  diagnostic  characters  of  the  powder: 

1.  Parenchyma  with  starch. 

2.  Dark  masses  of  epidermal  tissue. 

3.  Spigelia  should  contain  starch,  and  it  should  not  contain 
cystoliths,  stone  cells,  or  long,  white-walled  bast  fibres. 

POWDERED   RUELLIA   ROOT 

When  the  roots  of  ruellia  root  and  rhizome  are  powdered 
(Plate  94)  they  show  the  following  structure: 

The  epidermal  cells  vary  from  7.8  by  15.6  micromillimeters 


PLATE  93 


POWDERED  SPIGELIA  MARYLANDICA,  L. 

I.  Epidermis  and  cortical  parenchyma.  2.  Tracheids  and  fibres.  3.  Par- 
enchyma cells  of  the  root  containing  the  small  starch  grains,  longitudinal  view. 
4.  Parenchyma  of  the  rhizome  containing  the  large  starch  grains,  transverse 
view.  5.  Tracheids.  6.  Surface  view  of  the  epidermal  cells.  7.  Starch  scattered 
through  the  field.  8  and  8'.  Dark  masses  of  epidermal  and  underlying  tissue. 


PLATE  94 


POWDERED  RUELLIA  CILIOSA,  Pursh. 

I.  Short,  broad  cystoliths  from  the  rhizome,  i'.  Long  cystoliths  from  the 
root.  2  and  2'.  Long,  narrow,  white-walled  bast  fibres.  3.  Tracheal  tissue 
from  the  xylem  of  the  stem.  4.  Root  parenchyma.  5.  Tracheal  tissue  from 
the  xylem  of  the  root.  6.  Cortical  parenchyma  cells  from  the  rhizome  with 
short,  broad  cystoliths.  7  and  7'.  Long,  thick-walled  sclerids  from  the  root. 
8.  Short,  broad  sclerids  from  the  stem.  9.  Pitted  pith  parenchyma  from  the 
stem  with  intercellular  space.  10.  Parenchyma  of  the  root  with  sclerid  and 
cystolith,  longitudinal  view. 


230  HISTOLOGY   OF   MEDICINAL  PLANTS 

to  15.1  by  16.6  micromillimeters.  The  cell  contents  are  dark 
and  the  walls  are  light.  A  few  rows  of  the  outer  cortical  paren- 
chyma cells  of  both  the  rhizome  and  the  root  have  dark  cell 
contents  and  white  walls.  The  dark  contents  disappear  toward 
the  phloem.  The  cortical  cells  vary  from  13.6  by  14.3  micro- 
millimeters  to  89.5  by  90.9  micromillimeters.  In  the  cortical 
parenchyma  cells  of  the  rhizome  are  found  the  short,  broad 
cystoliths  measuring  up  to  52  by  62  micromillimeters.  In  the 
corresponding  cells  of  the  root  are  found  the  long,  narrow  cysto- 
liths which  measure  up  to  68.4  by  187.2  micromillimeters. 
Scattered  throughout  the  powder  are  seen  three  distinct  types 
of  sclerids  (stone  cells)  which  are  associated  with  the  cortical 
parenchyma  of  both  the  stem  and  the  root.  Most  of  them  are 
found,  however,  in  the  roots.  First,  the  short,  broad  stone 
cells  from  the  stem  basis  have  square  ends ;  the  walls  vary  from 
13  to  19.5  micromillimeters  in  thickness  with  branching  pores 
which  extend  toward  the  adjacent  cell.  These  sclerids  vary  in 
size  from  52  by  54.6  micromillimeters  to  45  by  130  micromilli- 
meters. Secondly,  the  long  stone  cells  from  the  root  vary  from 
32  by  96  micromillimeters  to  45.5  by  542.5  micromillimeters 
with  walls  1 6  micromillimeters  thick.  The  width  of  the  cell 
and  the  thickness  of  the  wall  vary  but  little  throughout  their 
entire  length.  The  third  type  of  stone  cell  also  from  the  root 
has  unequally  thickened  walls  and  the  ends  are  square  or  blunt. 
A  few  long,  narrow,  colorless,  thin- walled  bast  fibres  also  occur. 
They  are  13  micromillimeters  wide,  with  walls  3.9  micromilli- 
meters thick.  Annular  spiral  and  pitted  vessels  are  also  found 
scattered  throughout  the  powder. 

The  diagnostic  characters  of  the  powder  are: 

1.  The  short,  broad,  and  long,  narrow  cystoliths. 

2.  The  short,  broad,  and  long,  narrow  sclerids. 

3.  The  long,  narrow,  thin,  white-walled  bast  fibres. 

In  poke  root,  ipecac,  sarsaparilla,  and  veratrum  are  raphides. 
In  belladonna  and  horse-nettle  roots  are  micro-crystals.  In 
calumba,  stillingea,  krameria,  licorice,  scamony  root  are  prisms. 
In  saponaria,  jalap,  althea,  spikenard,  rumex,  rhubarb  are 
rosette  crystals.  In  pleurisy  roots  both  prisms  and  rosettes 
occur. 

In    gentian,    senega,    symphytuns,    lovage,    parsley,    inula, 


ROOTS   AND  RHIZOMES  231 

echinacea,  angelica,  burdock,  and  chicory  no  crystals  of  any 
kind  occur.  Root  hairs  occur  in  cross-sections  of  sarsaparilla 
root  and  false  unicorn,  but  with  these  exceptions:  root  hairs  do 
not  occur  on  roots,  because  the  younger  part  of  the  root  with 
root  hairs  is  not  removed  from  the  soil  when  the  drug  is  collected. 
In  sarsaparilla  root  there  are  several  layers  of  hypodermal  cells; 
in  most  roots  there  are  no  hypodermal  cells.  In  the  non- woody 
roots  or  the  roots  of  herbs  the  parenchyma  cells  form  the  greater 
part  of  the  tissues  of  the  root.  In  ruellia  root  are  stone  cells; 
in  spigelia  root  and  many  other  roots  there  are  no  stone  cells. 
In  ruellia  root  are  bast  fibres;  in  spigelia,  gentian,  ipecac,  chicory, 
dandelion,  symphytum,  and  lovage  no  bast  fibres  occur.  In 
all  the  woody  roots  there  is  a  periderm  consisting  of  typical 
cork  cells,  as  in  black  haw;  or  stone  cells,  as  in  asclepias;  or 
of  a  mixture  of  lifeless  parenchyma,  medullary  rays,  etc.,  as  in 
Oregon  grape  root. 

Woody  roots  have  a  phellogen  layer  which  is  absent  in  the 
non-woody  roots. 

The  numbers  of  layers  of  cortical  parenchyma  differ  in  the 
same  root  according  to  its  age,  but  for  a  given  root  there  is  a 
normal  variation. 

The  number  of  layers  of  cortical  parenchyma  in  proportion 
to  other  cells  is  less  in  woody  roots. 

In  woody  roots  there  is  no  endodermis.  The  cambium  in  these 
cases  shows  clearly  between  the  phloem  and  the  xylem  part  of 
the  fibro- vascular  bundle. 

In  woody  roots  the  wood  fibres  are  well  developed  and  form 
a  large  part  of  the  root,  and  the  medullary  rays  have  pitted 
side  and  end  walls. 

The  description  given  above  of  ruellia  root  is  not  typical  of 
all  roots,  but  the  structure  represents  the  greater  number  of 
the  elements  that  it  is  possible  to  find  in  a  root.  In  many  roots, 
for  instance,  there  are  no  stone  cells,  in  others  no  epidermis 
and  no  endodermis.  In  asclepias,  aconite,  and  calumba  stone 
cells  occur.  In  symphytum,  chicory,  dandelion,  burdock,  elecam- 
pane, pyre  thrum,  gentian,  and  senega  no  stone  cells  occur.  In 
aconite,  althea,  asclepias,  belladonna,  bryonia,  columba,  ipecac, 
jalap,  krameria,  sarsaparilla,  scamony,  stillingea,  and  rumex 
are  characteristic  starch  grains.  Symphytum,  chicory,  dande- 


232  HISTOLOGY   OF  MEDICINAL  PLANTS 

lion,  burdock,  elecampane,  and  pyrethrum  contain  inulin,  but 
no  starch.  In  saponaria,  gentian,  and  senega  neither  starch 
nor  inulin  occurs. 

When  studying  roots  the  nature  of  the  epidermis  or  the 
periderm  must  be  considered,  as  also  the  number  of  layers  of 
cortical  parenchyma;  the  occurrence,  distribution,  and  amount 
of  stone  cells  when  present;  the  presence  or  absence  of  the 
endodermis;  the  occurrence  and  structure  of  bast  fibres  when 
present;  the  nature  of  the  cambium  cells;  the  width  and  struc- 
ture of  the  medullary  rays,  the  size  of  the  wood  fibres  and  wood 
parenchyma,  and  the  nature  of  the  cell  contents  and  the  ar- 
rangement of  the  fibro- vascular  bundle. 


CHAPTER  II 

STEMS 

When  studying  stems  it  should  first  be  determined  whether 
they  were  derived  from  monocotyledonous  or  dicotyledonous 
plants.  This  fact  is  ascertained  by  determining  the  type  of 
the  fibro- vascular  bundle.  See  Chapter  XI.  The  next  fact 
to  determine  is  whether  the  stem  is  from  an  herb  or  from  a  woody 
plant.  This  fact  is  readily  determined  because  herbaceous 
stems  have  a  true  epidermis,  masses  of  collenchyma  at  the 
angles  of  the  stem.  The  cortical  cells  contain  chlorophyll,  and 
the  pith  is  very  large.  Woody  stems  have  a  corky  layer,  a 
phellogen  layer,  and  the  pith  is  very  small  except  in  the  very 
young  woody  stems. 

Having  determined  these  facts,  a  study  should  be  made  of 
the  arrangement,  form,  structure,  color,  and  the  cell  contents 
of  the  different  cells  in  order  to  determine  the  species  of  plant 
from  which  the  stem  was  obtained. 

HERBACEOUS   STEMS 

The  great  variation  in  the  structure  of  herbaceous  stems  is 
shown  in  the  cross-sections  of  spigelia  (Plate  95);  in  ruellia 
(Plate  96);  in  the  charts  of  powdered  genuine  horehound, 
powdered  spurious  horehound,  and  in  the  chart  of  powdered 
insect  flower  stems. 

CROSS-SECTION  SPIGELIA   STEM 

Spigelia  stem  (Plate  95)  has  the  following  characteristic 
structure : 

Epidermis.     The  epidermal  cells  are  papillate. 

Cortex.  The  cortical  parenchyma  cells  consist  of  tan- 
gen  tially  elongated  cells  which  are  oval  in  outline. 

Phloem.  The  phloem  consists  of  sieve  cells,  phloem  paren- 
chyma, and  c^f  bast  fibres. 

233 


PLATE  95 


u  // 

CROSS-SECTION  OF  STEM  OF  SPIGELIA  MARYLANDICA,  L. 

1.  Papillate  epidermis.  4.  Phloem.  7.  Inner  phloem. 

2.  (Cortical  parenchyma.  5.  Cambium.        ,  8.  Pith. 


3.  Bast  stereome. 


6.  Xylem. 


STEMS  235 

The  sieve  cells  are  small,  and  with  thin,  white,  angled 
walls. 

The  phloem  parenchyma  resembles  the  sieve  cells,  but  they 
are  larger. 

The  bast  fibres  are  rounded  in  outline  and  the  walls  are 
thick,  white,  non-porous,  and  non-striated. 

Cambium.  The  cambium  cells  are  rectangular  in  shape  or 
the  walls  are  collapsed  and  the  cells  indistinct. 

Xylem.  The  xylem  contains  vessels,  wood  parenchyma, 
medullary  rays.  The  vessels  are  small  and  angled,  the  walls 
are  thick  and  white. 

Wood  parenchyma.  The  cells  are  variable  in  size  and  shape, 
and  the  walls  are  thick.  The  medullary  ray  cells  are  small, 
narrow,  and  tangentially  elongated. 

Internal  Phloem.  External  to  the  pith  parenchyma  are 
isolated  groups  of  internal  phloem  consisting  of  sieve  cells. 

Pith  Parenchyma.  The  pith  parenchyma  cells  are  oval  in 
form  and  irregularly  placed.  The  cells  contain  small,  simple 
starch  grains. 

RUELLIA   STEM 

The  cross-section  of  ruellia  stem  (Plate  96)  is  as  follows: 

Epidermis.  The  epidermal  cells  are  variable  in  shape  and 
very  large.  There  are  no  cell  contents. 

Cortex.  The  cortex  consists  of  collenchyma  and  parenchyma 
cells  and  stone  cells. 

The  collenchyma  cells  have  very  small,  angled  cavities  and 
very  thick  walls.  These  cells  make  up  the  greater  part  of  the 
cortex. 

The  cortical  parenchyma  cells  are  variable  in  size  and  shape. 
The  stone  cells  occur  singly  or  in  groups.  The  walls  are  thick, 
white,  porous,  and  striated,  and  the  central  cavity  is  frequently 
quite  large. 

Phloem.  The  phloem  contains  sieve  cells,  phloem  paren- 
chyma, and  bast  fibres. 

The  sieve  cells  have  thin,  white,  angled  walls. 

The  phloem  parenchyma  cells  are  frequently  tangentially 
elongated,  otherwise  they  resemble  the  sieve  cells. 

The  bast  fibres  occur  alone  or  in  groups.  The  walls  are 
thick,  white  and  porous. 


PLATE  96 


io 


CROSS-SECTION  OF  STEM  OF  RUELLIA  CILIOSA,  Pursh. 

I.  Epidermis.     2.  Collenchyma.     3.  Parenchyma.     4.  Sclerids.     5.  Bast 
fibres.     6.  Phloem.     7.  Cambium  cells.     8.  Xylem.     io.  Pith  parenchyma. 


STEMS  237 

Cambium.  The  cambium  cells  are  rectangular  in  shape 
and  the  walls  are  thin. 

Xylem.  The  xylem  contains  vessels,  wood  parenchyma,  and 
medullary  rays. 

The  vessels  are  large;  the  walls  are  thick,  white,  and  angled. 

The  wood  parenchyma  cells  are  variable  in  size  and  shape 
and  the  walls  are  angled. 

The  medullary  ray  cells  are  radially  elongated  and  rectangu- 
lar in  shape. 

Pith  Parenchyma.  The  pith  parenchyma  cells  are  large  and 
rounded  in  shape. 

POWDERED  HOREHOUND 

The  structure  of  powdered  horehound  is  shown  in  Chart  97. 
The  epidermal  cells  of  the  leaf  (i)  are  wavy  in  outline,  the  guard 
cells  are  elliptical,  the  stoma  lens-shaped,  the  epidermis  often 
showing  hairy  outgrowth  as  in  the  illustration.  The  epidermal 
cells  of  the  petals  (2)  have  irregularly  thickened  beaded  walls. 
The  non-glandular  hairs  from  the  calyx  (3);  the  long,  thin- 
walled,  multicellular  non-glandular  twisted  hairs  (4)  from  the 
leaves  and  stems;  long,  thin-walled,  unicellular  hairs  (5)  from 
the  tube  of  the  corolla;  the  glandular  hairs  (6)  with  a  one-celled 
stalk  and  with  two  secreting  cells  divided  by  vertical  walls;  the 
eight-celled  glandular  hair  (7)  as  seen  in  surface  and  side  view; 
the  spiral  and  reticulated  conducting  cells  (8) ;  the  thick,  white- 
walled  fibres  from  the  stem  (9);  the  pollen  grains  (10)  with 
nearly  smooth  walls. 

The  diagnostic  elements  of  the  U.  S.  P.  horehound  are  the 
long,  twisted,  multicellular  hairs  (4),  the  glandular  hairs  (7), 
and  the  pollen  grains  (10). 

POWDERED   SPURIOUS  HOREHOUND 

Marrubium  perigrinum,  which  is  a  related  species  of  hore- 
hound and  which  is  a  common  adulterant  of  horehound,  has 
the  following  structure  (Plate  98) : 

The  wavy  leaf  epidermis  (i)  with  stoma;  the  beaded  wall 
petal  epidermis  (2);  the  non-glandular,  multicellular  branched 
hairs  (3)  from  the  stem  leaves  or  flowers;  the  broken  pieces  and 
branches  of  the  compound  hairs  (4)  scattered  throughout  the 


PLATE  97 


POWDERED  HOREHOUND  (Marrubium  vulgar e,  L). 

I.  Epidermis  of  leaf  showing  the  wavy  epidermal  cells,  stoma,  and  a 
clustered  hair.  2.  Surface  view  of  the  petal  epidermis.  3.  Non-glandular 
hair  from  the  calyx  or  corolla.  4.  Long,  thin-walled,  twisted,  non-glandular 
hairs  from  the  leaves  and  stem.  5.  Unicellular  non-glandular  hair  from  the 
tube  of  the  corolla.  6.  Glandular  hairs  with  a  one-celled  stalk  and  with  two 
secreting  cells  divided  by  vertical  walls.  7.  Surface  and  side  view  of  the 
eight-celled  glandular  hairs.  8.  Conducting  cells.  9.  Fibres  from  the  stem. 
10.  Pollen  grains. 


PLATE  98 


SPURIOUS  HOREHOUND  (Marrubium  peregrinum,  L.) 

i.  Surface  view  of  the  leaf  epidermis.  2.  View  of  the  petal  epidermis. 
3.  Non-glandular  multicellular  branched  hair  from  the  stem,  leaves,  or  flowers 
with  a  few  of  the  lower  branches  broken.  4.  Broken  pieces  and  branches  from 
the  compound  hairs  scattered  throughout  the  field.  5.  Unicellular  glandular 
hair  with  a  two-celled  stalk.  6.  Under-surface  view  of  an  eight-celled  gland- 
ular hair.  7.  Side  view  of  eight-celled  glandular  hair.  8.  Long,  pointed, 
unicellular,  non-glandular  hair  from  the  corolla,  the  wall  irregularly  thickened 
near  the  apex.  9.  Fibres.  10.  Pollen  grains,  n.  Conducting  cells  of  leaf. 


PLATE  99 


POWDERED  INSECT  FLOWER  STEMS  (Chrysanthemum  cinerariifolium, 
[Trev.],  Vis.) 

1.  Surface  view  of  epidermis.  5.  Cross-section  of  fibres. 

2.  Cross-section  of  epidermis.  6.  Longitudinal  view  of  pith  parenchyma. 

3.  Hairs.  7.  Cross-section  of  pith  parenchyma. 

4.  Fibres .  8.  Conducting  cells. 


•    STEMS  241 

field;  the  glandular  hairs  (5)  with  a  two-celled  stalk;  the  eight- 
celled  glandular  hair  (7)  seen  in  surface  view  and  a  side  view  (8) 
of  a  similar  hair;  the  long,  pointed,  unicellular  non-glandular 
hair  from  the  tube  of  the  corolla,  the  wall  irregularly  thickened 
near  the  apex;  the  fibres  (9)  from  the  stem;  the  pollen  grains 
(10)  with  prominent  centrifugal  projections;  the  conducting 
cells. 

The  diagnostic  elements  of  marrubium  perigrinum  are  the 
multicellular  branched  hairs  (3)  which  occur  on  all  parts  of  the 
plant,  usually  much  broken  in  the  powder,  with  walls  many 
times  thicker  than  the  walls  of  the  hairs  found  in  U.  S.  P.  hore- 
hound;  the  pollen  grains  (10)  with  centrifugal  projections  and 
the  stalked  glandular  hairs  (5). 

INSECT  FLOWER  STEMS 

Insect  flower  stems  are  the  chief  adulterant  of  insect  flowers. 
Until  the  passage  of  the  insecticide  law,  it  was  a  common  practice 
to  sell  (for  insect  powder)  a  mixture  of  powdered  stems  and 
flowers.  Since  the  passage  of  the  law,  the  presence  of  the  stems 
in  a  powder  is  supposed  to  be  declared  on  the  label.  In  spite 
of  the  penalties  attached,  their  presence  in  a  powder  is  frequently 
not  declared,  as  evidenced  by  a  microscopical  examination  of 
the  insect  powders  obtained  in  the  open  market. 

The  structure  of  powdered  insect  flower  stems  (Chart  99)  is 
as  follows: 

The  epidermal  cells  of  the  stems  are  prominently  marked 
with  stoma  and  angled,  striated  wall  cells  (Fig.  i).  On  cross- 
section  (Fig.  2)  the  stem  is  seen  to  be  made  up  of  epidermal 
cells  with  thick  outer  and  thin  side  walls  (Fig.  2) .  The  T-shaped 
hairs  (Fig.  3)  are  longer  than  those  found  on  any  other  part  of 
the  plant.  The  fibres  (Fig.  4)  are  the  most  characteristic  part 
of  the  powder.  They  are  elongated,  and  the  walls  are  white 
and  slightly  porous  and  of  nearly  uniform  thickness.  They 
occur  free  in  the  field  or  in  groups  of  two  or  more.  The 
cross-section  view  of  these  fibres  is  shown  in  Fig.  5.  The  pith 
parenchyma  (Fig.  6)  is  abundant  and  is  composed  of  thick, 
porous- walled  cells.  On  cross-section  the  cells  are  rounded 
and  are  separated  by  intercellular  spaces.  The  conducting  cells 
(Fig.  8)  vary  from  spiral  to  reticulate. 


CHAPTER   III 
WOODY   STEMS 

BUCHU    STEM 

The  cross-section  of  a  buchu  stem  (Plate  C),  1.6  millimeters 
in  diameter,  shows  a  few  of  the  epidermal  cells  modified  into 
thick- walled,  roughish,  unicellular  trichomes  (i).  The  remain- 
ing epidermal  cells  have  a  thick,  wavy  outer  wall  (2).  Beneath 
the  epidermis  are  several  rows  of  cortical  parenchyma  cells  (3) 
which  extend  to  the  bast  bundles  and  in  which  are  found  the 
secretory  cavities  with  the  thin- walled  secretory  cells  (4).  The 
bast  fibres  (5)  occur  in  continuous  bands,  varying  greatly  in  size; 
the  walls  are  whitish  and  of  variable  thickness.  Inside  the 
bast  fibres,  the  small  irregular  sieve  cells  (6)  occur  in  groups, 
surrounded  by  the  phloem  parenchyma  (8).  The  radially 
elongated  cells  of  the  medullary  rays  (7)  extend  outward  from 
the  xylem,  increasing  in  number  in  the  outer  portions  of  the 
wood,  and  extending  nearly  to  the  bast  fibres.  No  distinct 
cambium  layer  is  visible.  The  conducting  cells  (9)  occur 
throughout  the  xylem  surrounded  by  the  wood  fibres  and  wood 
parenchyma  (10).  The  latter  is  not  very  abundant  in  buchu. 
The  medullary  rays  border  on  the  conducting  cells  and  extend 
outward  to  the  phloem.  The  pith  parenchyma  cells  are  nearly 
circular  in  outline  and  often  show  a  perforated  end  wall  when 
a  cell  happens  to  be  cut  just  above  or  below  that  point. 

MATURE   BUCHU   STEM 

In  Plate  loi-A  is  shown  the  cork  formation  or  secondary 
growth  as  seen  in  the  older,  larger  buchu  stems.  The  wavy 
epidermis  (i),  which  is  the  primary  epidermis  and  which  has 
disappeared  on  many  portions  of  the  stem,  has  thin  side  walls 
and  dark  cell  contents  (2).  Next  to  the  epidermal  cells  occur 
several  rows  of  peculiarly  arched  cork  cells  with  thick,  white 
outer  walls  (3)  and  reddish-brown  cell  contents  (4).  The  cork 

242 


PLATE   100 


11 


v^ 

CROSS-SECTION  OF  BUCHU  STEMS  (Barosma  betulina  [Berg.],  Earth,  and  Wendl.) 

i.  Hairs.      2.  Wavy  epidermis.      3.  Cortical  parenchyma.      4.  Secretion 

cells  and  cavity.     5.  Group  of  bast  fibres.     6.  Sieve  cells.     7.  Medullary  rays. 

™loem  parenchyma.     9.  Vessels.     10.  Wood  fibres,  and  wood  parenchyma. 

II.  Pith  parenchyma. 


PLATE   101 


A.  Cross-section  of  buchu  stem    (Barosma    betulina   [Berg.],   Barth.   and 
Wendl.).     i,  Outer  wall  of  epidermis;   2,  Cell  cavity  of  epidermal  cell;   3,  Wall 
of  cork  cell;   4,  Cavity  of  cork  cell;    5,  Phellogen  layer;    6,  Divided  phellogen 
cell  changing  into  a  cortical  parenchyma  cell;    7,  Cortical  parenchyma  cell. 

B.  Cross-section  of  leptandra  rhizome   (Leptandra  virginica  [L.],  Nutt.). 
i,  Parenchyma  cells  undergoing  change  in  the  composition  of  their  walls;   2,  A 
break  in  the  epidermal  tissue;   3,  Parenchyma  cells  undergoing  division. 


WOODY   STEMS  245 

cambium  (5)  is  typical  in  form,  and  it  has  formed  one  or  two 
layers  of  phelloderm  cells  (6)  which  have  the  same  form  as  the 
cambium  cells  but  with  thicker  walls.  Next  to  the  phelloderm 
occur  the  cortical  parenchyma  cells.  The  remaining  structure 
of  the  mature  stem  is  identical  with  that  of  Fig.  2. 

POWDERED   BUCHU   STEM 

Powdered  buchu  stem  (Plate  102)  has  many  striking  features 
which  make  it  easy  of  identification  when  mixed  with  buchu 
leaves.  A  few  unicellular,  rough,  thick,  white-walled  trichomes 
(i)  occur  distributed  throughout  the  field.  They  are  straight 
or  slightly  curved  and  vary  in  length  from  40  to  100  microns; 
in  thickness  at  the  bast  they  measure  from  10  to  22  microns. 
The  central  cavity  varies  greatly,  and  in  some  trichomes  seems 
to  have  disappeared  entirely.  The  epidermal  cells  (2)  are  very 
characteristic,  occurring  singly  or  in  groups  of  two  or  more. 
The  cells  from  the  older  stems  often  appear  reddish  brown  by 
transmitted  light,  while  the  epidermal  cells  from  the  younger 
stems  appear  whitish  opaque  (porcelain-like) .  They  are  usually 
six-sided  and  angular  in  outline.  The  cortical  parenchyma 
cells  (3)  on  transverse  view  have  a  rounded  cell  cavity  and 
intercellular  spaces  between  the  walls.  The  double  walls  vary 
in  thickness,  the  greatest  thickness  being  about  9  microns.  The 
parenchyma  cells  (3)  on  longitudinal  view  show  square  ends 
and  often  contain  sphaero-crystalline  masses  of  hesperidin.  The 
thin-walled  sieve  cells  and  the  surrounding  cells  are  scarcely 
ever  seen  in  the  powder.  The  white-walled  pointed  stereomes 
(4)  are  a  characteristic  feature  of  the  powder;  they  vary  greatly 
in  length,  in  diameter  and  in  the  thickness  of  their  walls.  In 
a  number  eighty  powder  the  fibres  are  mostly  broken.  The 
greatest  length  of  the  unbroken  fibres  is  1.25  microns.  The 
thickest  wall  measured  5  microns  and  the  greatest  observed 
width  was  25  microns.  The  spiral  reticulate  and  scalariform 
thickened  conducting  cells  occur  scattered  throughout  the 
powder.  The  reticulate  and  scalariform  cells  usually  occur  with 
wood  fibres.  It  is  an  interesting  fact  that  the  spiral  thickening 
in  conducting  cells  is  usually  separate  from  the  side  wall  and 
nearly  always  appears  as  indicated  at  5.  An  occasional  rosette 
crystal  of  calcium  oxalate  (6)  is  seen  in  the  field.  The  wood 


PLATE    102 


POWDERED  BUCHU  STEMS  (Barosma  betulina  (Berg.],  Barth.  and  Wcndl.). 

I.  Hairs.  2.  Epidermal  cells,  the  larger  pieces  reddish-brown;  the  smaller 
aggregations  white.  3.  Transverse  cortical  parenchyma.  3'.  Longitudinal 
cortical  parenchyma  with  sphaero  crystalline  masses  of  hesperidin.  4.  Bast 
fibres.  5.  Spiral,  sclariform,  and  reticulate  vessels.  6.  Rosette  crystals  of 
calcium  oxalate.  7.  Wood  parenchyma.  8.  Pith  parenchyma  with  porous 
side  and  end  walls.  9.  Wood  fibres. 


WOODY   STEMS  247 

parenchyma  (7),  which  makes  up  a  very  small  percentage  of 
the  xylem,  is  not  readily  found  in  the  powder.  The  pith  paren- 
chyma cells  (8)  have  thick,  porous  side  walls  and  perforated  side 
walls.  The  wood  fibres  (9)  usually  occur  in  masses  surrounding 
the  conducting  cells;  when  occurring  singly,  the  oblique  pores 
readily  distinguish  them  from  the  bast  fibres. 

The  diagnostic  elements  of  powdered  buchu  stems  are: 
First,  trichomes;   secondly,  reddish-brown  and  white-angled 
epidermal  cells;  thirdly,  the  long,  white  bast  fibres. 


CHAPTER  IV 

BARKS 

Barks  are  all  obtained  from  dicotyledonous  plants.  In 
studying  barks  there  should  be  ascertained  the  thickness,  ar- 
rangement, form,  structure,  color,  and  cell  contents  of  the  cells 
occurring  in  the  outer,  middle,  and  inner  barks. 

The  outer  bark  includes  the  cork  cells  and  the  phellogen 
layer.  The  middle  bark  includes  all  the  cells  occurring  between 
the  phellogen  layer  and  the  beginning  of  the  medullary  rays. 
The  inner  bark  includes  the  medullary  ray  cells  and  all  cells 
associated  with  them.  The  plan  of  structure  of  all  barks  is 
similar,  but  in  each  species  of  plant  the  structure  of  the  bark 
is  uniform  and  characteristic  for  the  species. 

A  great  number  of  drugs  consist  of  the  bark  of  woody  plants ; 
for  this  reason  the  bark  is  considered  in  a  separate  chapter  from 
the  stem. 

WHITE   PINE   BARK 

The  cross-section  of  white  pine  bark  (Plate  103)  has  the 
following  structure: 

Outer  Bark.  The  periderm  consists  of  several  layers  of 
reddish-brown  cork  cells  (i)  which  are  narrow,  elongated,  and 
with  thin  walls. 

Middle  Bark.  The  cells  forming  the  middle  bark  are  paren- 
chyma and  secretion  cells. 

The  parenchyma  cells  vary  greatly  in  size,  form,  and  thick- 
ness of  the  walls.  The  cells  beneath  the  cork  cells  and  around 
the  secretion  cells  are  tangentially  elongated  and  oval  in  shape, 
while  the  other  parenchyma  cells  are  more  irregular  in  shape. 

The  secretion  cells  are  arranged  around  the  schizogenous 
secretion  cavities.  The  cells  are  tangentially  elongated,  and  the 
walls,  which  are  slightly  papillate,  are  white. 

Inner  Bark.  The  cells  forming  the  inner  bark  are  medullary 
rays,  parenchyma,  sieve  cells,  and  storage  cavities. 

248 


PLATE   103 


10 


CROSS-SECTION  OF  UNROSSED  WHITE  PINE  BARK  (Pinus  strobus,  L.) 

i.  Cork  cells  of  the  epidermis.  2.  Parenchyma  cells  filled  with  chlorophyl. 
3.  Intercellular  space.  4.  Secretion  cavity  with  resin.  5.  Secretion  cells. 
6,  One  or  more  circles  of  parenchyma  filled  with  chlorophyl.  7.  Parenchyma. 
8.  Meduilary  rays.  9.  Sieve  cells.  10.  Storage  cavities. 


250  HISTOLOGY   OF  MEDICINAL  PLANTS 

The  medullary  rays  form  wavy  lines.  The  medullary  ray 
cells  are  radially  elongated,  rectangular  in  shape,  and  they  con- 
tain granular  cell  contents.  The  sieve  cells  are  either  square 
or  rectangular  in  shape.  The  walls  are  thin  and  white.  The 
storage  cavities  are  either  filled  with  starch  or  with  prisms 
and  tannin. 

POWDERED  WHITE  PINE  BARK 

White  pine  bark  (Plate  104)  when  powdered  shows  the 
following  characteristic  elements: 

The  microscopic  structure  of  a  powdered  white  pine  is  as 
follows:  The  epidermis  (i)  consists  of  reddish-brown  masses, 
irregular  in  outline.  The  outer  parenchyma  cells  are  of  a  bright- 
green  color,  owing  to  the  presence  of  chlorophyll.  (The  above 
elements  are  not  usually  found  in  the  rossed  bark.)  The  paren- 
chyma (3)  with  starch  usually  occurs  in  longitudinal  sections 
accompanied  with  sieve  cells.  Often  the  tissue  separates  trans- 
versely, showing  the  medullary  rays  (4)  with  their  granular  cell 
contents  (9)  and  the  inner  parenchyma  cells  filled  with  starch 
and  the  surrounding  sieve  cells. 

The  crystals  are  nearly  perfect  cubes  and  occur  singly  (5) 
or  in  groups  (6).  On  the  longitudinal  section  of  the  bark  the 
crystals  occur  in  parenchyma  cells  surrounded  by  a  reddish  cell 
content  and  form  parallel  rows  which  are  very  characteristic. 
The  resin  occurs  either  as  white,  angled  fragments  (7)  in  a  water 
mount,  or  as  globular  mass  (8)  or  as  reddish-brown  pieces  (10). 
The  starch  is  very  abundant  and  is  distributed  through  the 
field.  The  diagnostic  grain  is  lens-shaped,  with  a  cleft  hilum, 
which  is  nearly  straight,  or  slightly  curved,  and  runs  parallel 
to  the  long  diameter  of  the  grain.  The  addition  of  ferric 
chlorid  T.  S.  will  show  the  presence  of  tannin  by  forming  a 
dark  coloration.  The  identification  of  the  starch  is  facilitated 
by  the  addition  of  a  weak  Lugol's  solution,  which .  imparts  a 
blue  coloration  to  the  starch  grain. 

The  form,  amount,  and  distribution  of  the  cells  composing 
the  bark  differ  greatly  in  different  plants. 

In  cramp  bark  the  cork  and  phellogen  cells  are  very  large, 
while  in  cascara  sagrada  the  phellogen  and  the  cork  cells  are 
very  small. 


PLATE   104 


POWDERED  WHITE  PINE  BARK  (Pinus  strobus,  L.) 

i.  Epidermis.  2.  Parenchyma  cells.  3.  Parenchyma  with  starch.  4. 
Medullary  rays.  5.  Solitary  crystals.  6.  Solitary  crystals  and  tannin.  7,  8 
and  10.  Resin  masses.  9.  Starch. 


252  HISTOLOGY  OF  MEDICINAL  PLANTS 

In  canella  alba  bark  the  periderm  is  composed  of  stone- 
cell  cork  or  stone  cells  arranged  in  superimposed  rpws,  which 
form  the  outer  layers  of  the  bark. 

In  white  oak  and  most  barks  from  woody  trees  the  periderm 
consists  of  lifeless  parenchyma,  medullary  rays,  sieve  cells, 
bast  'fibres,  and  in  some  cases  stone  cells  and  of  phellogen 
cells. 

In  young  wild  cherry,  cascara  sagrada,  and  frangula  are 
several  layers  of  tangentially  elongated  collenchyma  cells  with 
chlorophyll.  In  the  older  barks  of  the  above  and  in  many 
other  barks  no  collenchyma  cells  occur. 

In  cramp  bark  and  in  tulip  tree  bark  the  outer  layers  of  the 
cortical  parenchyma  cells  are  beaded.  In  most  barks  there  is 
no  beaded  walled  parenchyma.  The  outer  layers  of  most 
cortical  parenchyma  cells  are  tangentially  elongated  while  the 
inner  parenchyma  cells  are  mostly  circular  in  outline. 

In  white  oak,  cascara  sagrada  and  prickly  ash  are  groups 
of  stone  cells;  in  the  cinnamon  barks  are  bands  of  stone  cells; 
in  cinchona  bark  are  isolated  stone  cells.  In  cramp  bark, 
mezerum,  elm,  and  white  pine  bark  no  stone  cells  occur. 

In  frangula,  cascara  sagrada,  cocillina,  cinnamon,  cinchona, 
sassafras,  and  wild  cherry  barks  the  bast  fibres  occur  in  groups. 
In  frangula,  cascara  sagrada,  and  cocillina  the  bast  fibres  are 
surrounded  by  crystal  cells  with  crystals. 

In  sassafras  bark  mucilage  cells  occur.  In  canella  alba, 
white  pine,  and  sassafras  barks  secretion  cells  occur;  but  in 
most  barks  no  secretion  cells  occur. 

In  sassafras  bark  the  medullary  ray  cells  are  nearly  as  broad 
as  long;  in  cramp  bark  they  are  elongated  and  oval  in  shape. 
In  cascara  sagrada,  as  in  most  barks,  the  cells  are  longer  than 
broad  and  rectangular  in  shape. 

In  cascara  sagrada  the  sieve  cells  are  very  large ;  in  granatum 
bark  the  sieve  cells  are  very  small. 

In  cassia  cinnamon  and  in  canella  alba  bark  the  walls  of  the 
sieve  cells  have  collapsed,  with  the  result  that  the  sieve  cells 
have  become  partly  obliterated. 

In  witch-hazel,  mountain  maple,  willow,  and  black  walnut 
are  found  prisms;  in  cramp  bark,  black  haw,  wahoo,  pome- 
granate, and  cotton  root  bark  arc  found  rosette  crystals;  in 


BARKS  253 

the  cinnamon  barks  are  found  raphides;  in  cinchona  bark, 
micro-crystals. 

In  cocillina,  frangula,  cascara  sagrada,  white  oak,  poplar 
and  Jamaica  dogwood  barks  are  found  crystal-bearing  fibres 
(Plates  19  and  20). 

When  studying  barks  we  must  consider  the  kind,  structure, 
and  amount  of  the  periderm;  the  nature  of  the  phellogen;  the 
nature  and  amount  of  the  cortical  parenchyma;  the  occurrence, 
distribution,  and  amount  of  stone  cells,  when  present;  the 
occurrence  and  structure  of  the  bast  fibres;  the  presence  or 
absence  of  secretion  cells;  the  width,  distribution,  and  structure 
of  the  medullary  rays. 


CHAPTER  V 

WOODS 

Quite  a  number  of  drugs  consist  of  the  wood  of  woody  plants; 
such  drugs  are  quassia,  red  saunders,  white  sandalwood,  and 
guaiac. 

When  studying  woods  it  is  necessary  to  observe  the  cross, 
tangential,  and  radial  sections.  Such  sections  of  quassia  are 
shown  in  Plates  105,  106,  and  107.  When  studying  these  sec- 
tions it  should  be  remembered  that  while  the  types  of  cells  form- 
ing quassia  wood  are  similar  to  the  cells  forming  other  woods, 
still  their  structure,  arrangement,  and  amount  will  vary  in  a 
recognizable  way  in  the  different  woods. 

CROSS-SECTION  QUASSIA 

Plate  105  is  a  cross-section  of  quassia.  It  has  the  following 
structure : 

Vessels.  The  vessels  occur  singly  or  in  groups  of  two  to 
eight  cells.  The  cells  are  variable  in  size  and  shape.  The 
walls  are  yellowish  white  and  porous. 

Medullary  Rays.  The  medullary  rays  vary  from  one  to  five 
cells  in  width. 

The  medullary  ray  cells  are  radially  elongated  and  the  walls 
are  strongly  porous. 

Wood  Parenchyma.  The  wood  parenchyma  cells  have  thin, 
yellowish- white,  angled  walls. 

Wood  Fibres.  The  wood  fibres  have  thick,  yellowish-white, 
angled  walls.  These  cells  are  smaller  in  diameter  than  the 
wood  parenchyma  cells. 

RADIAL  SECTION  QUASSIA 

The  radial  section  of  quassia  (Plate  107)  is  as  follows: 
Vessels.     The  vessels  appear  as  in  the  tangential  section. 
Medullary   rays.     The   medullary   rays   vary   from   ten   to 

254 


PLATE  105 


CROSS-SECTION  OF  QUASSIA  WOOD  (Picrana  excelsa  [Sw.],  Undl.) 

1.  Vessels. 

2.  Medullary  rays. 

3.  Wood  parenchyma. 

4.  Wood  fibres. 


PLATE    1 06 


TANGENTIAL  SECTION  OF  QUASSIA  WOOD  (Picrana  excelsa  [Sw.],  Lindl.) 

i.  Vessel.     2.  Wood  parenchyma.     3.  Wood  fibre.     4.  End  wall  of  med- 
ullary ray  cell.     5.  Medullary  ray  bundle. 


PLATE    107 


RADIAL  SECTION  OF  QUASSIA  WOOD  (Picrana  excelsa  [Sw.],  Lindl.) 

1.  Showing  the  height  and  length  of  the  medullary  rays  and  cells. 

2.  Cells  with  starch. 

3.  Wood  parenchyma  and  wood  fibres. 


258  HISTOLOGY   OF   MEDICINAL  PLANTS 

twenty  cells  in  height  according  to  the  part  of  the  medullary 
ray  bundle  cut  across. 

The  medullary  ray  cells  exhibit  their  height  and  length. 
The  walls  of  the  cells  are  yellowish  white  and  strongly 
porous. 

Wood  Parenchyma.  The  wood  parenchyma  cells  have 
yellowish,  thin  walls  and  blunt  end  walls. 

Wood  Fibres.  The  wood  fibres  have  thick,  yellowish-white 
walls,  and  the  end  of  the  cells  are  strongly  tapering. 

TANGENTIAL   SECTION  QUASSIA 

The  tangential  section  of  quassia  (Plate  106)  shows  the 
following  structure: 

Vessels.  The  vessels  are  very  long  and  broad  and  the 
yellow  walls  are  marked  with  clearly  defined  pits. 

Medullary  Rays.  The  tangential  section  shows  the  cross- 
section  of  the  medullary  ray  bundle  and  the  cross-section  of 
the  medullary  ray  cell. 

The  medullary  ray  bundle  varies  in  width  from  one  to  five 
cells.  The  ends  of  the  bundles  are  always  one  cell  in  width, 
while  the  central  part  of  the  bundle  is  frequently  five  cells 
in  width. 

The  medullary  ray  cell  varies  in  size,  structure,  and  shape 
according  to  the  part  of  the  cell  cut  across.  The  cells  cut 
across  the  centre  show  hollow  spaces,  but  the  cells  cut  just 
above  or  below  the  end  wall  show  a  strongly  pitted  surface. 
The  cells  forming  the  end  of  the  bundle  are  larger  than  the  cells 
forming  the  centre  of  the  bundle. 

Wood  Parenchyma.  The  wood  parenchyma  cells  are  greatly 
elongated  and  the  walls  are  thin  and  yellowish  white.  The 
ends  of  the  cells  are  blunt. 

Wood  Fibres.  The  wood  fibres  are  elongated,  the  walls 
are  thick  and  the  cells  are  strongly  tapering. 

In  quassia,  white  sandalwood,  red  sandalwood,  and  guaiac 
wood  are  characteristic  crystals. 

In  quassia  the  vessds  are  finely  pitted,  yellowish,  and  dis- 
tinct; in  white  sandalwood  the  vessels  are  coarsely  and  sparingly 
pitted  and  white  translucent;  in  red  saunders  the  vessels  are 
coarsely  pitted,  bright  red  and  distinct. 


WOODS  259 

When  studying  woods  we  must  consider  the  width  of  the 
medullary  rays,  the  structure  and  cell  contents  of  the  medullary 
ray  cells;  the  structure,  color,  and  cell  contents  of  the  wood 
parenchyma;  also  the  wood  fibres. 


CHAPTER  VI 

LEAVES 

Leaves  collectively  constitute  the  greatest  manufacturing 
plant  in  the  world.  Most  of  the  food,  clothing,  and  medicine 
used  by  man  is  formed  as  a  result  of  the  work  of  the  leaf.  The 
cell  contents,  structure,  and  arrangement  of  the  different  cells 
of  the  leaf  differ  in  a  marked  degree  from  the  cell  contents, 
structure,  and  arrangement  of  the  cells  in  the  other  organs  of 
the  plant.  This  accounts  for  the  presence  of  the  large  amount 
of  chlorophyll  in  the  leaf,  the  presence  of  stomata,  and  the 
peculiar  arrangement  of  the  cells. 

It  should  be  ascertained  if  the  stomata  are  above,  even  with, 
or  below  the  epidermis;  the  nature  of  the  epidermal  cells,  and, 
when  present,  the  nature  of  the  hypodermal. cells;  the  number  of 
layers  of  palisade  parenchyma  and  whether  it  is  present  on 
both  surfaces  of  the  leaf,  and  the  nature  of  the  outgrowths  from 
the  epidermal  cells. 

KLIP   BUCHU 

The  cross-section  of  klip  buchu  (Plate  108)  has  the  following 
structure : 

Epidermis.  The  epidermal  cells  of  klip  buchu  are  modified 
to  form  papillae,  the  walls  are  yellowish  white,  and  the  papillate 
portion  of  the  cell  is  nearly  solid. 

Hypodermis.  The  hypodermal  cells  are  never  intact  because 
the  mucilage  contained  in  the  cells  swells  when  placed  in  water 
and  breaks  the  thin  side  walls. 

Upper  Palisade  Parenchyma.  The  palisade  parenchyma  is 
two  layers  in  thickness.  The  cells  of  the  outer  layer  are  greatly 
elongated  and  are  packed  with  chlorophyll.  The  inner  layer 
of  palisade  cells  is  more  irregular,  and  the  cells  are  much  shorter 
than  the  cells  of  the  outer  palisade  layer. 

Spongy  Parenchyma.  The  spongy  parenchyma  cells  are 

260 


PLATE   1 08 


CROSS-SECTION  OF  KLIP  BUCHU  JUST  OVER  THE  VEIN 

A .  Papillate  upper  epidermis. 

B.  Hypodermal  cells  with  broken  side  walls,  due  to  expansion  of  mucilage 
contents. 

C.  Palisade  cells,  showing  two  cells  filled  with  chlorophyll. 

D.  Palisade  like  mesophyll. 

E.  Endodermis. 

F.  Vascular  strand  of  vein. 

G.  Conducting  cells  with  spirally  thickened  walls. 
H.  Characteristic  leaf  mesophyll. 

/.    Short,  thick  palisade  cells  on  the  under  side  of  leaf,  just  under  the  vein. 
/.    Under  hypodermal  cells. 
K.  Papillate  under  epidermis. 


262  HISTOLOGY   OF  MEDICINAL  PLANTS 

branched;  therefore,  large  intercellular  spaces  occur  between 
the  cells. 

Under  Palisade  Parenchyma.  The  palisade  cells  of  the 
under  epidermis  are  short  and  broad,  and  they  contain  fewer 
chlorophyll  grains  than  the  upper  palisade  cells  of  the  upper 
epidermis.  These  cells  occur  only  under  the  veins. 

Under  Hypodermis.  The  under  hypodermal  cells  are  shorter 
and  broader  than  the  upper  hypodermal  cells. 

Under  Epidermis.  The  under  epidermal  cells  are  modified 
to  form  papillae  which  are  similar  to  the  papillae  of  the  upper 
epidermis. 

Fibro-Vascular  Bundle.  The  cells  composing  the  vascular 
bundle  are  sieve  cells,  vessels,  and  fibres. 

The  sieve  cells  are  small  and  the  walls  are  white  and 
angled. 

The  vessels  have  thick,  white,  angled  walls. 

The  bast  fibres  are  rounded  in  outline  and  the  walls  are  thick 
and  white. 

Endodermis.  The  endodermal  cells  encircle  the  fibro-vascu- 
lar  bundles.  The  cells  are  large,  thin-walled,  and  oval  in  shape. 

Secretion  Cells.  Near  the  edges  of  the  leaf  are  schizoge- 
nous  secretion  cavities  surrounded  by  thin-walled  secretion 
cells. 

POWDERED   KLIP   BUCHU 

When  the  leaf  is  powdered  (Plate  109),  the  cells  are  quite 
as  characteristic  in  appearance.  The  upper  epidermal  cells 
(i)  have  thick-beaded,  yellowish- white  walls  and  papillate  outer 
walls.  No  stomata  occur  on  the  upper  surface.  The  under 
epidermis  (2)  with  numerous  stomata,  is  surrounded  by  the 
characteristic  guard  cells.  The  end  walls  are  beaded  as  on  the 
upper  surface.  The  palisade  cells  (3)  appear  as  in  the  cross- 
section.  The  conducting  cells  (4  and  4)  are  of  the  spiral  and 
pitted  type.  The  papillae  (5  and  5)  are  very  abundant  in  the 
powder  and  very  characteristic.  The  fragments  of  the  epidermis 
(6)  are  also  abundant.  The  mesophyll  (7)  is  characteristic,  as 
it  retains  its  form  when  powdered.  The  fibres  (8)  are  usually 
associated  with  the  conducting  cells;  occasionally  they  are 
found  free  as  in  the  illustration. 


PLATE   109 


POWDERED  KLIP  BUCHU 

I.  Upper  epidermis.  2.  Under  epidermis.  3.  Palisade  cells  with  chloro- 
phyll. 4  and  4.  Conducting  cells.  5  and  5.  Papillae.  6.  Fragments  of  the 
epidermis.  7.  Mesophyll.  8.  Fibres. 


204  HISTOLOGY    OP    MEDICINAL   PLANTS 


MOUNTAIN  LAUREL 

Epidermis.  The  epidermal  cells  of  mountain  laurel  are  oc- 
casionally modified,  as  unicellular  hairs  (Plate  no.  Fig.  i), 
particularly  in  the  region  of  the  veins.  The  ordinary  epidermal 
cells  have  thick  outer  walls  and  thin  inner  walls.  Beneath 
many  of  the  epidermal  cells  are  large  air-spaces. 

Upper  Palisade  Parenchyma.  The  palisade  parenchyma 
vary  from  four  to  five  layers.  The  inner  palisade  cells  are 
shorter  and  broader  than  the  outer  layer  of  cells. 

Parenchyma.  The  parenchyma  cells  (Fig.  4)  are  rounded 
in  form  and  they  are  arranged  in  the  form  of  columns  which  are 
one  cell  in  thickness  above,  but  two  to  three  cells  in  thickness 
near  the  under  epidermis.  Between  each  chain  of  cells  is  a 
larger  intercellular  space  (Fig.  6) .  In  a  few  of  the  cells  are  large 
rosette  crystals. 

Under  Epidermis.  The  under  epidermal  cells  are  uniformly 
smaller  than  the  upper  epidermal  cells. 

It  is  thus  seen  that  mountain  laurel  leaf  has  no  hypodermal 
cells;  no  spongy  parenchyma;  no  under  palisade  cells;  no  under 
hypodermal  cells,  and  no  secretion  cavities. 

TRAILING  ARBUTUS 

Epidermis.  The  epidermal  cells  of  the  trailing  arbutus 
(Plate  in,  Fig.  2)  are  variable  in  size.  Many  of  the  cells  are 
modified,  as  guard  cells  (Fig.  i). 

Parenchyma.  The  parenchyma  cells  are  round  and  they 
are  compactly  arranged  (Fig.  3)  on  the  upper  side  of  the  leaf, 
but  on  the  under  side  they  are  arranged  in  round,  small,  intercel- 
lular spaces  (Fig.  5).  In  some  of  the  intercellular  spaces  are 
rosette  crystals  (Fig.  7). 

Under  Epidermis.  The  under  epidermal  cells  are  smaller 
than  the  upper  epidermal  cells. 

It  will  be  seen  that  the  structure  of  trailing  arbutus  leaf  is 
very  simple  and  that  its  structure  is  different  from  that  of  klip 
buchu  and  mountain  laurel. 

The  structure  of  powdered  leaves  is  very  variable,  yet  char- 
acteristic for  a  given  species.  The  leaves  from  the  insect  flower 
plant  are  collected  with  the  stems,  and  ground  and  sold  as  a 


PLATE    1 10 


CROSS-SECTION  MOUNTAIN  LAUREL  (Kalmia  latifolia,  L.) 

I.  Hair.     2.  Epidermis.     3.  Palisade  parenchyma.     4.  Parenchyma.     5. 
Under  epidermis.    6.  Intercellular  space.    7.  Rosette  crystal.    8.  Chlorophyll. 


PLATE    in 


DQQOC 


DOGDDoBffl 


CROSS-SECTION  TRAILING  ARBUTUS  LEAF  (Epigaa  repens,  L.) 

I.  Stomata.     2.  Epidermis.     3.  Parenchyma.     4.  Cell  with  chlorophyll, 
5.  Intercellular  space.     6.  Under  epidermis.     7.  Rosette  crystal. 


LEAVES  267 

substitute  for  insect  flowers.  These  leaves,  when  powdered, 
show  the  following  structure  (Plate  112): 

Both  the  upper  and  lower  epidermis  have  stomata  (Figs, 
i  and  2),  but  they  differ  in  that  the  surrounding  cells  of  the 
upper  epidermis  are  wavy,  while  the  corresponding  cells  of  the 
under  epidermis  are  similar,  though  the  under  epidermis  has 
many  attached  hairs  (Figs.  3  and  4).  The  T-shaped  hairs  form 
the  most  abundant  element  of  the  powder.  They  are  similar 
in  structure  to  those  found  on  the  scales  and  stem.  Fragments 
of  the  mesophyll  have  round  cells  and  contain  chlorophyll 
(Fig.  6).  The  conducting  cells  are  spiral  or  reticulate. 

The  different  cells  of  the  leaf  differ  greatly  in  structure,  in 
amount,  and  in  arrangement.  In  uva-ursi,  boldus,  pilocarpus, 
eucalyptus,  and  chimaphila  leaves  the  outer  walls  of  the  epidermal 
cell  is  very  thick.  In  uva-ursi  leaves  this  thick  wall  appears 
bluish  green  when  viewed  under  low  power  of  the  microscope. 

In  belladonna,  stramonium,  henbane,  peppermint,  spear- 
mint, digitalis,  and  horehound,  the  outer  wall  of  the  epidermal 
cells  is  thin. 

In  witch-hazel,  stramonium,  coca,  phytolacca,  and  pepper- 
mint there  is  a  single  layer  of  palisade  parenchyma  on  the 
upper  surface  only  of  the  leaf. 

In  senna  there  is  one  layer  of  palisade  parenchyma  on 
the  upper  and  one  layer  on  the  under  side  of  the  leaf.  In 
matico  and  tea  leaves  there  are  two  layers  of  spongy  parenchyma 
on  the  upper  side  of  the  leaf. 

In  chestnut  leaves  there  are  three  layers  of  palisade  paren- 
chyma on  the  upper  side  of  the  leaf. 

In  eucalyptus  leaves  the  entire  central  part  of  the  leaf, 
with  the  exception  of  the  secretion  cells  and  nbro-vascular 
bundle,  is  made  up  of  the  palisade  parenchyma. 

In  some  leaves  no  palisade  parenchyma  occurs.  Trailing 
arbutus  (Plate  in)  is  an  example  of  such  a  leaf. 

In  stramonium  leaves  the  spongy  parenchyma  is  strongly 
branched;  in  mountain  laurel  the  spongy  parenchyma  is 
mostly  non-branched  and  circular  in  form,  as  in  trailing  arbutus 
(Plate  in,  Fig.  3),  and  as  occurs  in  the  midrib  portion  of  most 
leaves. 

In    stramonium    and     chestnut     are    found    rosette    crys- 


PLATE    112 


POWDERED  INSECT  FLOWER  LEAVES 
'(Chrysanthemum  cinerariifolium  [Trev.],  Vis.) 

*    rrossr1?'"1'8;      2'  -Vnder  cP.idermis  Bowing  stonui  and  hair  scar. 
Cross-section  of  under  epidermis  with  attached  hair.      4    Cross-section  of 

<  Hairs- 


LEAVES  269 

tals.  In  henbane,  coca,  and  senna  are  found  prisms.  In  bella- 
donna, scapola,  and  tobacco  leaves  are  found  micro-crystals. 
In  most  leaves  no  crystals  occur.  In  witch-hazel  and  tea 
leaves  stone  cells  occur,  but  in  most  leaves  there  are  no  stone 
cells.  In  eucalyptus,  thyme,  jaborandi,  buchu,  rosemary,  and 
white  pine  leaves  are  secretion  cells;  while  in  belladonna, 
stramonium  cells  occur.  In  senna  and  coca  leaves  are  crystal- 
bearing  fibres;  most  leaves  do  not  have  crystal-bearing  fibres. 

In  chimaphila  and  uva-ursi  there  are  no  outgrowths  from 
the  epidermal  cells. 

In  senna,  witch-hazel,  chestnut,  and  coca,  numerous  non- 
glandular  hairs  occur  on  the  epidermis.  In  tobacco,  belladonna, 
henbane,  pennyroyal,  peppermint,  and  spearmint  both  glandular 
and  non-glandular  hairs  occur  on  the  epidermis.. 

When  studying  leaves  there  should  be  considered  the  ab- 
sence or  presence  of  outgrowths  and  their  nature;  the  nature  of 
the  epidermis  and,  wrhen  present,  the  number  of  layers  of  the 
hypodermis;  the  nature  of  the  stoma,  whether  raised  above, 
even  with,  or  below  the  level  of  the  epidermis;  the  number  of 
layers,  and  the  distribution,  when  present,  of  the  palisade 
parenchyma;  the  form  and  amount  of  the  spongy  parenchyma; 
the  absence  or  presence  of  secretion  cells;  the  nature  and  form 
of  the  fibro-vascular  bundles,  and  the  nature  and  amount  of 
the  organic  and  inorganic  cell  contents. 


CHAPTER  VII 

FLOWERS 

The  histological  structure  of  flowers  is  readily  seen  in  the 
powder;  therefore,  in  studying  flowers,  it  is  not  necessary  to 
section  the  various  parts.  Each  part  of  the  flower  should  be 
isolated  and  powdered  separately  and  each  separated  part 
studied.  In  each  case  the  powders  will  contain  surface,  cross-, 
and  radial  sections  of  the  parts  powdered.  While  studying 
flowers,  special  attention  should  be  given  to  the  pollen  grains, 
to  the  papillae  of  the  petals,  to  the  papillae  of  the  stigma,  and, 
in  certain  flowers,  to  the  style  tissue.  In  the  composite  flowers 
special  attention  should  also  be  given  to  the  involucre  scales, 
to  the  scales  of  receptacle,  and,  when  present,  to  the  pappus. 
In  addition,  attention  must  be  given  to  secretion  cavities,  as 
in  cloves. 

POLLEN   GRAINS 

Pollen  grains  are  one  of  the  most  characteristic  elements 
found  in  powdered  flowers,  because  they  are  so  small  that  they 
are  not  broken  up  when  the  drug  is  milled. 

The  two  principal  groups  of  pollen  grains  are,  first,  those  with 
non-spiny  walls  (Plate  113);  and,  secondly,  those  with  spiny 
walls  (Plate  114),  as  shown  in  the  two  charts. 

In  lavender  flowers  the  pollen  grains  have  six  constrictions 
of  the  outer  wall.  This  wall  is  slightly  striated  and  the  cell 
contents  are  granular. 

In  clover  flowers  the  pollen  grains  are  mostly  rounded  in 
outline,  the  wall  is  uniformly  thickened,  and  cell  contents  are 
coarsely  granular. 

In  belladonna  flowers  the  pollen  grains  terminate  in  three 
blunt  points. 

In  Spanish  saffron  the  pollen  grains  are  spherical  and  the 
cell  contents  are  granular. 

270 


PLATE   113 


9 


SMOOTH-WALLED  POLLEN  GRAINS 

i.  Cloves  (Eugenia  caryophyllata,  Thunb.).  2.  Santonica  (Artemisia 
pauciftora,  Weber).  3.  Elder  (Sambucus  canadensis,  L.)-  4-  Century  minor 
(Erythraa  centaurium  [L.],  Pers.).  5.  Pichi  (Fabiana  imbricata,  R.  and  P.). 
6.  Cyani.  7.  Lavender  (Lavandula  officinalis,  Chaix.).  8.  Clover  (Trifolium 
pratense,  L.).  9.  Belladonna  (Atropa  belladonna,  L.).  10.  Spanish  saffron 
(Crocus  sativus,  L.). 


PLATE   114 


SPINY  WALLED  POLLEN  GRAINS 

1.  Anthemis  (Anthemis  nobilis,  L.). 

2.  Arnica  (Arnica  montana,  L.). 

3.  Calendula  (Calendula  officinalis,  L.). 

4.  Cassia  flowers. 

5.  American  saffron  (Carthamus  tinctorius,  L.). 

6.  Blue  malva  flowers  (Malva  sylvestris,  L.). 


FLOWERS  273 

The  non-spiny-walled  pollen  grains  differ  not  only  in  micro- 
scopic appearance,  but  also  in  size.  Clove  pollen  grains  are 
the  smallest,  while  Spanish  saffron  pollen  grains  are  the  largest. 

NON-SPINY-WALLED   POLLEN   GRAINS 

In  cloves  the  pollen  grains  show  a  six-sided,  angled  cavity 
and  an  outer  wall  which  terminates  in  three  slightly  pointed, 
narrowly  notched  portions,  separated  by  nearly  straight  walls. 

In  santonica  the  pollen  grains  have  smooth,  unequally 
thickened  walls,  which  are  strongly  constricted  at  three  points, 
the  outline  resembling  three  half-circles  placed  together. 

In  elder  flowers  the  pollen  grains  appear  circular  or  three- 
parted.  The  wall  is  of  nearly  uniform  thickness,  even  at  the 
constricted  part  of  the  grain. 

In  century  minor  the  pollen  grains  show  three  pronounced 
restrictions.  The  wall  at  these  points  is  very  thin.  In  pichi 
flowers  the  pollen  grains  are  either  circular  or  three-sided  and 
three-pointed.  Inside  of  each  point  there  is  a  nearly  white  pore. 
In  some  of  the  grains  the  pollen  tube  has  grown  out  of  one  of 
the  pores. 

In  cyani  flowers  tne  pollen  grains  are  longer  than  broad  and 
the  cell  contents  appear  to  be  divided  into  two  end  portions 
and  an  elevated  middle  portion 

SPINY-WALLED   POLLEN   GRAINS 

In  anthemis  the  pollen  grains  have  unequally  thickened 
walls  constricted  in  three  places.  The  spines  are  short,  broad 
at  the  base,  and  sharp-pointed. 

In  arnica  flowers  the  pollen  grains  show  three  light-colored 
pores  and  numerous  short  spines. 

In  calendula  flowers  the  pollen  grains  show  one  or  more 
pores,  typically  three  pores.  These  pores  appear  as  white  spots, 
and  the  wall  immediately  over  the  pore  is  smooth  and  thinner 
than  the  remaining  part  of  the  wall;  the  spines  are  very  numerous. 

In  cassia  flower  pollen  grains  the  outer  wall  is  extended  into 
a  number  of  rounded  projections  which  are  frequently  arranged 
in  sets  of  fours. 

In  American  saffron  flowers  the  pollen  grains  show  one,  two, 
or  three  light-colored  pores;  the  spines  are  short  and  broad. 


274  HISTOLOGY  OF  MEDICINAL  PLANTS 

In  blue  malva  flowers  the  pollen  grains  are  spherical  and  the 
outer  wall  extends  into  numerous  spinelike  projections. 

It  will  be  observed  that  the  spiny- walled  pollen  grains  differ 
greatly  in  size,  the  smallest  being  the  pollen  grain  of  anthemis 
and  the  largest  being  the  pollen  grain  of  blue  malva 
flowers. 

In  matricaria  are  numerous,  greenish-brown,  spiny-walled 
pollen  grains.  In  anthemis  are  multicellular,  uniseriate  non- 
glandular  hairs  with  three  or  four  short,  broad,  yellow- 
walled  basal  cells  and  a  greatly  elongated,  thin,  gray-walled 
apical  cell. 

In  arnica  are  multiseriated  branched  hairs  of  the  pappus, 
and  numerous  large,  yellowish,  spiny-walled  pollen  grains. 

STIGMA  PAPILLAE 

The  papillae  of  the  stigma  of  most  flowers  form  a  character- 
istic element  even  when  the  flower  is  powdered.  In  the  case 
of  composite  flowers  the  papillae  of  the  disk  and  ray  flowers 
differ.  In  American  saffron  the  papillae  of  the  style  differ  in  a 
recognizable  way  from  the  papillae  of  the  stigma. 

The  papillae  of  the  stigma  of  the  ray  and  disk  flowers  of 
arnica,  anthemis,  matricaria,  and  insect  flowers  differ  greatly. 
Even  the  papillae  of  the  stigma  of  the  ray  and  disk  flowers  differ. 
In  all  cases  observed  the  papillae  of  the  ray  flowers  are  smaller 
than  the  papillae  of  the  disk  flowers. 

The  papillae  of  the  stigma  of  saffron  (Plate  115,  Fig.  3)  are 
long  and  tubular.  These  papillae  are  nearly  uniform  in  diam- 
eter, and  the  apex  is  blunt  and  rounded.  The  wall  is  slightly 
granular  in  appearance.  The  papillae  of  the  stigma  of  American 
saffron  (Plate  116,  Fig.  2)  are  short  and  tubular.  Each  papilla 
is  broadest  at  the  base  and  tapers  to  a  slender  point.  The 
papillae  of  that  part  of  the  style  which  emerges  from  the  corolla 
(Plate  116,  Fig.  i)  are  large  and  curved,  and  the  walls  are  very 
thick.  The  apex  of  the  papilla  is  frequently  solid. 

The  papillae  of  the  stigma  of  the  ray  flowers  of  anthemis 
(Plate  117,  Fig.  i)  have  thin,  slightly  striated  walls;  while  the 
papillae  of  the  stigma  of  the  disk  flowers  (Plate  117,  Fig.  2)  are 
longer,  the  walls  are  thicker,  and  the  cell  content  is  denser. 

The  papillae  of  the  stigma  of  the  ray  (Plate  117,  Fig.  3)  and 


PLATE   115 


PAPILLAE 

1.  Arnica  ray  flowers  (Arnica  montana,  L.). 

2.  Insect  flower  disk  (Chrysanthemum  dnerariifolium  [Trev.],  Vis.). 

3.  True  saffron  (Crocus  sativus,  L.) 


PLATE   116 


PAPILLAE  OF  STIGMAS 

1.  Stigma  papillae  of  American  saffron  (Carihamus  tinctorius,  L.)  from  that 
part  of  the  style  that  emerges  from  the  corolla. 

2.  Papillae  from  the  upper  part  of  the  stigma  of  American  saffron. 

3.  Papillae  of  the  stigma  of  the  disk  flowers  of  arnica  (Arnica  nwtitnna,  L.). 


PLATE   117 


PAPILL/E  OF  STIGMAS 


2      rt/^^^  L) 

2.  Stigma  papUbe  of  the  tubular  flowers  of  anthemis. 

milla,  If™  PaP  the  HgUlatC  fl°Wers  of 

4-  Stigma  papillae  of  the  disk  flowers  of  matricaria. 

°f  i 


278  HISTOLOGY   OF  MEDICINAL  PLANTS 

disk  flowers  (Plate  117,  Fig.  5)  of  matricaria  are  similar  in 
structure,  but  the  papillae  of  the  disk  flowers  are  larger. 

The  papillae  of  the  stigma  of  the  ligulate  flowers  of  insect 
flowers  (Plate  117,  Fig.  5)  are  tubular;  the  walls  are  striated, 
and  in  each  papilla  there  is  a  small  yellow  globule,  while  the 
papillae  of  the  disk  flowers  (Plate  115,  Fig.  2)  are  long  and 
tubular,  and  the  walls  are  thick. 

The  papillae  of  the  stigma  of  the  ray  flowers  of  arnica  (Plate 
115,  Fig.  i)  are  very  short  and  tubular.  The  walls  are  thin 
and  the  cell  contents  appear  as  small,  bright-yellow  globules, 
while  the  papillae  of  the  stigma  of  the  disk  flowers  (Plate  116, 
Fig.  3)  are  broadest  at  the  base,  the  apex  is  pointed,  and  the 
yellow  globules  are  larger. 

The  solitary  hairs  are  divided  into  the  branched  and  non- 
branched  hairs. 

POWDERED  INSECT  FLOWERS 

The  microscopic  examination  of  insect  powder  is  difficult  for 
the  reason  that  there  are  so  many  elements  to  be  constantly 
kept  in  mind.  The  parts  of  the  flower  which  contribute  char- 
acteristic cells  are  the  stem,  involucre,  ray  flowers,  disk  flowers, 
and  the  receptacle.  In  each  of  these  parts  there  are  many 
different  types  of  cells. 

There  are  practically  two  types  of  flowers  found  in  insect 
powder  of  commerce:  first,  closed  or  immature  flowers,  and 
secondly,  open  or  mature  flowers.  As  explained  above,  the 
half-open  flowers  consist  largely  of  the  two  above-named  varie- 
ties. Let  us  first  consider  the  structure  of  the  closed  insect 
flowers  as  illustrated  in  Plate  118. 

The  involucre  has  many  characteristic  cells.  The  more 
prominent  ones  seen  in  the  powder  are  the  edge  of  the  scale  with 
the  attached  hair  (Fig.  i).  These  hairs  (Fig.  3)  are  T-shaped. 
The  terminal  cell  is  expanded  laterally,  and  it  terminates  in 
two  points.  Connecting  the  terminal  cell  with  the  epidermis 
are  two  or  three  cells  which  are  slightly  longer  than  broad. 
In  the  powder  the  terminal  cell  is  usually  attached  to  fragments 
only  of  the  supporting  cells.  Fibres  of  the  bracts  have  thick, 
wavy,  porous  walls,  and  they  have  a  tendency  to  occur  in  masses. 
The  upper  epidermis  (Fig.  4)  of  the  ray-flower  petal  is  promi- 


PLATE    118 


10 


POWDERED  CLOSED  INSECT  FLOWER 
(Chrysanthemum  cinerarnfolium,  [Trev.]  Vis.) 

I.  Edge  of  scale.  2.  Fibre  of  scale.  3.  Hairs.  4.  Upper  epidermis  of 
ray  flower.  5.  Under  epidermis  of  ray  flower.  6.  Cross-section  of  ray  petal. 
7.  Parenchyma  of  ray  flowers  with  crystals.  8.  Lobe  of  disk  petal.  9.  Filament 
tissue.  10.  Calyx  tissue,  n.  Lobe  of  stamen.  12.  Pollen.  13.  Papillae  of 
stigma.  14.  Secretion  cavity  with  surrounding  cells.  15.  Parenchyma  of 
the  receptacle. 


280  HISTOLOGY   OF   MEDICINAL   PLANTS 

nently  papillate.  The  under  epidermis  consists  of  wavy  cells 
without  papillae.  Another  view  of  the  papillae  is  shown  in 
Fig.  6.  The  parenchyma  of  the  ray  flowers  (Fig.  7)  contain 
cubical  crystals.  The  lobe  *  of  the  disk-flower  petal  (Fig.  8) 
is  papillate  at  the  end,  the  terminal  cells  have  thick  outer  and 
thin  inner  walls.  The  filament  tissue  (Fig.  9)  is  composed  of 
nearly  square  cells.  The  calyx  tissue  (Fig.  10)  is  made  up  of 
thin- walled  cells  with  slightly  papillate  margins.  The  lobe  of  the 
stamen  (Fig.  n)  consists  of  nearly  uniform  epidermal  cells 
which  are  in  contact'  throughout  their  long  diameter,  while  the 
hypodermal  cells  are  thin-walled  and  angled.  The  pollen  grains 
(Fig.  12)  are  dark  yellowish  green,  thin,  and  the  wall  does  not 
appear  perforated  by  pores.  The  papillae  of  the  stigma  (Fig.  13) 
are  clustered,  club-shaped,  and  nearly  white  in  color.  They 
are  usually  found  detached  in  the  powder.  All  parts  of  the 
pistil  contain  secreting  cells,  but  the  most  conspicuous  secreting 
cavities  (Fig.  14)  are  those  of  the  ovary.  These  cavities  appear 
brownish  in  color  and  are  surrounded  by  small  cells  which  appear 
indistinct  on  account  of  the  great  number  of  superimposed  cells. 
The  parenchyma  of  the  receptacle  occurs  in  fragments  which 
have  strongly  marked  porous  walls. 

OPEN  INSECT  FLOWERS 

Many  of  the  structures  of  open  insect  flowers  (Plate  119) 
are  similar  to  those  found  in  the  closed  flower.  There  is  prac- 
tically no  difference  in  the  edge  of  the  scale  (Fig.  i);  or  the 
fibre  of  the  scale  (Fig.  2) ;  or  the  T-shaped  hairs  (Fig.  3) ;  or  the 
upper  epidermis  of  the  ray  flower  (Fig.  4) ;  or  the  under  epidermis 
of  the  ray  flower  (Fig.  5) ;  or  the  cross-section  of  the  ray  petal 
(Fig.  6);  or  the  lobe  of  the  disk  petal  (Fig.  7);  or  the  filament 
tissue  (Fig.  8) ;  or  the  lobe  of  the  stamen  (Fig.  9) ;  or  the  papillae 
of  the  stigma  (Fig.  12);  or  the  parenchyma  of  the  receptacle 
(Fig.  15).  The  difference  in  structure  is  found,  first,  in  the 
involucre  scales,  which  are  more  fibrous  than  the  scales  of  the 
closed  flowers;  secondly,  in  the  pollen  (Fig.  n),  which  is  less 
abundant  than  in  the  closed  flower;  it  is  also  lighter  in  color 
and  usually  shows  the  wall  perforated  by  three  pores;  thirdly, 
the  outer  layers  of  the  achene  consist  of  thick,  porous- walled 
stone  cells  (Fig.  13),  which  occur  singly  or  in  groups;  fourthly, 


PLATE   119 


12 


14 


POWDERED  OPEN  INSECT  FLOWER 
(Chrysanthemum  cinerariijolium,  [Trev.]  Vis.) 

I.  Edge  of  involucre  scale.  2.  Fibres  of  involucre  scale.  3.  Hairs. 
4.  Upper  epidermis  of  ray  flower.  5.  Under  epidermis  of  ray  flower. 
6.  Cross-section  of  ray  petal.  7.  Lobe  of  disk  flower.  8.  Filament  tissue. 
9.  Lobe  of  stamen.  10.  Calyx  tissue,  n.  Pollen.  12.  Papillae  of  the  stigma. 
13.  Stone  cells  from  the  achene  and  cross-section  of  achene.  14.  Secretion 
cavity  with  surrounding  cells.  15.  Parenchyma  of  the  receptacle. 


282  HISTOLOGY  OF  MEDICINAL  PLANTS 

the  secretion  cavity  is  broader  and  darker  in  color  (Fig.  14). 
These  differences  enable  one  at  once  to  distinguish  between 
the  closed  and  open  insect  flowers.  Now,  since  the  half-closed 
flowers  consist  almost  wholly  of  a  mixture  of  equal  parts  of 
closed  and  open  flowers,  it  follows  that  the  elements  of  these 
two  flowers  will  be  mixed  in  about  equal  proportions.  Thus 
we  are  able  to  distinguish  microscopically  the  three  commercial 
varieties  of  insect  powder — namely,  closed  insect  flowers,  open 
insect  flowers,  and  half-open  insect  flowers. 

Insect  flowers  are  the  most  valuable  vegetable  insecticide 
known;  yet  much  of  its  effectiveness  is  destroyed  by  the  adulter- 
ants which  are  so  readily  identified  by  the  compound  microscope. 

POWDERED   WHITE  DAISIES 

A  common  adulterant  found  in  open  insect  flowers  is  the 
flower-heads  of  European  daisy  (C.  leucanthemum) .  Examination 
of  powdered  flowers  exported  from  Europe  shows  that  the  entire 
flower-head  is  ground  and  mixed  with  the  insect  flowers.  In 
the  cheaper  varieties  of  open  flowers,  only  the  tubular  flowers 
are  added  after  they  have  been  separated  from  the  heads  by 
crushing  and  sifting.  These  tubular  flowers  so  closely  resemble 
the  tubular  flowers  of  the  true  insect  flowers  that  it  is  practically 
impossible  to  distinguish  between  them  macroscopically.  The 
quickest  and  surest  way  to  identify  them  is  to  reduce  a  portion 
of  the  flowers  to  a  fine  powder  and  examine  it  microscopically. 

Certain  structures  of  the  white  daisies  (Plate  120)  are  some- 
what similar  to  those  found  in  insect  flowers.  These  structures 
are  the  papillae  of  the  ray  petal  (Figs.  3,5,  and  13),  the  lobe  of 
the  disk  petal  (Fig.  14),  and  the  lobe  of  the  stamen  and  the 
pollen  (Fig.  8). 

The  differences  are  as  follows:  The  under  epidermis  of  the 
ray  flowers  is  composed  of  wavy  cells  which  are  more  elongated 
than  the  ray  flowers  of  the  under  epidermis  of  the  ray  petal  of 
insect  flower.  The  filament  tissue  is  made  up  of  slightly  beaded 
cells  instead  of  smooth-walled  cells.  The  papillae  of  the  stigma 
are  smaller  than  the  papillae  of  insect  flowers.  The  most  striking 
difference  is  found  in  the  structure  of  the  achene.  The  epidermal 
tissue  of  the  achene  is  composed  of  palisade  cells  (Fig.  10),  which 
in  the  mature  form  have  thick  white  walls  and  scarcely  any 


PLATE   120 


POWDERED  WHITE  DAISIES  (Chrysanthemum  leucanthemum,  L.) 

i  and  2.  Scale  tissue.  3,  5  and  13.  Papillae  of  petals.  4.  Scale  tissue. 
6.  Lobe  of  ray  petal.  7.  Filament  tissue.  8.  Pollen.  9.  Papilla  of  stigma. 
10.  Palisade  cells  of  achene.  II.  Resin  masses.  12.  Parenchyma  of  recep- 
tacle. 14.  Lobe  of  dish  petal. 


284  HISTOLOGY   OF  MEDICINAL  PLANTS 

cavity.  These  cells  swell  perceptibly  when  placed  in  water. 
The  other  striking  feature  of  the  achene  is  the  bright  red  resin 
masses  which  occur  free  in  the  field.  Even  a  small  trace  of 
daisies  in  insect  powder  can  be  identified. 

When  studying  flowers  there  should  be  considered  the  number 
and  structure  of  pollen  grains;  the  nature  of  the  papillae  of  the 
stigma  and  the  petals;  the  nature  of  the  hairs  of  the  corolla  and 
calyx,  when  present.  In  the  composite  flowers  we  should  also 
consider  the  structure  of  the  involucre  scales,  and,  when  present, 
the  structure  of  the  receptacle  scales,  as  in  the  case  of  anthemus, 
and  of  the  pappus  hairs,  as  in  the  flowers  of  arnica,  boneset, 
grindelia,  and  aromatic  goldenrod. 


CHAPTER  VIII 

FRUITS 

There  is  great  variation  in  the  structure  of  fruits,  such  a 
variation,  in  fact,  that  no  one  fruit  has  a  structure  typical  of 
all  the  other  fruits.  Each  fruit,  however,  has  a  pericarp  and 
one  or  mo1  re  seeds.  The  amount  and  structure  of  the  cells 
forming  the  pericarp  and  the  seeds  of  fruits  differ  in  different 
fruits,  but  for  each  fruit  there  is  a  normal  amount  of,  and  a 
characteristic,  cellular  structure.  Nearly  all  the  important 
medicinal  fruits  are  cremocarps  .or  umbelliferous  fruits. 

The  plan  of  structure  of  cremocarps  is  similar,  but  they  all 
have  a  different  cellular  structure.  The  epidermis  may  be 
simple  or  modified  as  papillae  or  hairs.  The  secretion  cavities 
may  be  absent  (conium),  or,  when  present,  variable  in  number 
— cultivated  celery  seed  has  six,  wild  celery  seed  up  to  twelve, 
and  anise  up  to  twenty.  The  vascular  bundles  may  be  large  or 
small.  The  endocarp  cells  may  be  two  or  more  layers  in  thick- 
ness. The  spermoderm  may  be  thin  or  thick. 

The  endosperm  cells  may  vary  in  size  and  the  cell  contents 
may  vary. 

CELERY  FRUIT 

The  fruit  of  celery  (Plate  121),  like  other  umbelliferous 
fruits,  is  composed  of  the  pericarp  and  the  seed. 

The  pericarp  is  composed  of  epicarp  cells,  mesocarp  cells, 
endocarp  cells,  and  in  each  rib  a  vascular  bundle.  The  seed  is 
composed  of  the  spermoderm,  endosperm,  and  embryo.  Each 
of  these  parts  has  a  characteristic  structure. 

Epicarp.  The  cells  of  the  epicarp  (Fig.  i)  are  papillae  and  the 
outer  wall  is  striated.  The  papillae  do  not  show,  however,  unless 
the  cell  is  cut  across  the  centre,  which  is  the  point  at  which  the 
papillae  are  located. 

Mesocarp.  In  the  rib  part  of  the  mesocarp  (Fig.  2)  is  a 

285 


PLATE  121 


CROSS-SECTION  OF  CELERY  FRUIT  (Apium  graveolens,  L.) 
i.  Epicarp      2.  Mesocarp.     3.  Vascular  bundle.     4.  Endocarp. 
5.  bpermoderm.     6.  Endosperm.     7.  Secretion  cavity. 


PLATE   122 


DIAGRAMMATIC  DRAWING  OF  THE 

1.  Cross-section  of  wild  celery  seed  (Apium  graveolens,  L.). 

2.  Cross-section  of  cultivated  celery  seed  (Apium  graveolens,  L.). 


288  HISTOLOGY   OF   MEDICINAL  PLANTS 

vascular  bundle,  and  between  the  ribs  one  or  more  secretion 
cavities.  The  vascular  bundles  are  small  and  are  surrounded  by 
irregular-shaped  mesocarp  cells. 

The  secretion  cavities  (Fig.  7)  are  oval  in  form  and  the  tissue 
bordering  the  cavity  is  reddish  brown  in  color.  The  mesocarp 
cells  around  the  secretion  cavities  are  more  elongated  than  the 
other  mesocarp  cells. 

En  do  car  p.  The  endocarp  cells  are  three  layers  in  thickness. 
These  cells  are  elongated  transversely  (Fig.  4). 

Spermoderm.  The  cells  of  the  spermoderm  are  indistinct, 
compressed,  and  dark  brown  in  color  (Fig.  5). 

Endosperm.  The  endosperm  cells  (Fig.  6)  make  up  the  greater 
part  of  the  fruit.  The  walls  which  are  common  to  two  cells 
are  thick,  non-beaded,  and  non-pitted,  and  the  cavities  of  the 
cells  are  filled  with  aleurone  grains. 

Embryo.  The  embryo  cells,  which  show  only  in  certain 
sections,  are  similar  to  endosperm  cells. 

In  anise,  hops,  sumac,  and  cumin  fruits  are  characteristic 
hairs. 

In  star  anise,  sabal,  allspice,  cubeb,  pepper,  juniper,  buck- 
thorn, and  phytolacca  fruits  are  stone  cells. 

In  cubeb,  pepper,  and  cardamon  are  characteristic  masses  of 
aggregate  starch. 

In  sabal,  allspice,  and  juniper  are  characteristic  secretion  cells. 

In  all  the  umbelliferous  fruits,  with  the  exception  of  conium, 
are  yellow  to  brown  secretion  cavities. 

In  cubeb  and  pepper  is  aggregate  starch.  Colocynth  con- 
tains many  single  and  double  spiral  vessels. 

Bitter  orange  contains  solitary  crystals  and  spongy  par- 
enchyma. 

When  studying  fruits  we  must  consider  the  nature  of  the 
epicarp  cells — whether  simple  or  modified  as  papillae  or  hairs; 
the  form  and  structure  of  the  mesocarp  cells;  the  number,  size, 
and  structure  of  the  vascular  bundle;  the  size  and  number  of 
the  secretion  cells  or  cavities;  the  number  of  layers  and  the 
structure  of  the  endocarp  cells;  the  number  of  layers  of  stone 
cells— when  present;-  the  color  and  width  of  the  spermoderm 
layer;  the  structure  and  cell  contents  of  the  endosperm  cells; 
the  nature  of  the  embryo  cells,  and  the  nature  of  the  cell  contents. 


CHAPTER  IX 

SEEDS 

Seeds  are  very  variable  in  structure,  so  much  so,  in  fact, 
that  scarcely  any  two  seeds  have  a  similar  structure.  It  is 
necessary,  therefore,  when  examining  seeds,  to  compare  the  struc- 
ture of  the  seed  under  examination  with  authentic  plates  or 
with  the  section  of  a  genuine  seed.  The  layers  of  the  seed 
are  the  spermoderm,  perisperm,  endosperm,  and  embryo.  In 
some  seeds  the  spermoderm  forms  the  greater  part  of  the  seed; 
in  others  the  perisperm  is  greatest  in  amount;  in  still  others 
the  cotyledons  make  up  most  of  the  seed,  as  in  the  mustards. 
The  cells  forming  these  different  layers  differ  in  form,  structure, 
and  number;  therefore  it  is  not  difficult  to  distinguish  and  to 
differentiate  between  the  different  seeds  when  viewed  as  a  sec- 
tion or  as  a  powder.  Almond  is  studied  because  it  has  most  of 
the  layers  and  cells  found  in  seeds. 

SPERMODERM 

•The  spermoderm  is  the  thin,  brown,  granular-appearing 
skin  of  the  almond.  The  layers  of  the  spermoderm  are  the 
epidermis,  the  hypoderm,  the  middle  layers,  and  the  inner 
epidermis. 

The  epidermis  consists  of  radially  elongated,  thick- walled 
stone  cells  which  occur  alone  or  in  groups  of  two  or  more,  but 
seldom  as  a  continuous  layer.  The  upper  or  outer  part  of  the 
stone  cells  is  non-porous,  but  the  inner  walls  are  strongly  porous 
(Plate  123,  Fig.  i). 

The  hypoderm.  The  cells  forming  the  hypoderm  are  com- 
pressed, the  wall  structure  is  practically  indistinguishable,  and 
the  whole  mass  is  reddish  brown  (Plate  123,  Fig.  2). 

Occurring  in  this  brown  layer  are  several  vascular  bundles 
(Plate  123,  Fig.  3). 

289 


PLATE   123 


CROSS-SECTION  SWEET  ALMOND  SEED 

I.  Epidermis.  2.  Hypoderm.  3.  Vascular  bundle.  4.  Middle  layer. 
5.  Inner  epidermis.  6.  Endosperm.  7.  Outer  layer  of  the  embryo.  8.  Inner 
layers  of  the  embryo. 


SEEDS  *291 

The  middle  layers.  The  cells  forming  the  middle  layers 
(Fig.  4)  have  thin,  wavy,  light-colored  walls  which  are  frequently 
compressed,  and  it  is  with  much  difficulty  that  their  outlines 
are  made  out. 

The  inner  epidermis.  The  cells  forming  the  inner  epidermis 
are  rectangular  in  form,  and  they  contain  reddish-brown  cell 
contents  (Plate  123,  Fig.  5). 

ENDOSPERM 

The  endosperm.  The  cells  forming  the  endosperm  are  large, 
rectangular  in  outline,  usually  one  layer  thick,  and  they  contain 
aleurone  grains. 

EMBRYO 

The  embryo.  The  cells  forming  the  outer  layer  of  the  em- 
bryo are  smaller  than  the  inner  layers,  and  they  are  immediately 
inward  from  the  layer  of  endosperm  cells  (Plate  123,  Fig.  7). 

The  cells  forming  the  greater  part  of  the  embryo  are  large, 
rounded,  and  they  contain  aleurone  grains  and  fixed  oil  (Plate 
123,  Fig.  8). 

In  white  and  black  mustard  are  characteristic  mucilage  and 
palisade  cells. 

In  nux  vomica,  stropanthus,  and  St.  Ignatius's  bean  are 
characteristic  hairs. 

In  physostigma  and  kola  are  characteristic  starch  grains. 

In  henbane,  capsicum,  stramonium,  lobelia,  and  belladonna 
seeds  are  characteristic  epidermal  cells. 

In  areca  nut,  colchicum,  saw  palmetto,  and  nux  vomica  are 
characteristic  thick-walled,  reserve  cellulose  cells. 

In  cardamon  seed  are  aggregate  starch  masses  with  irregular 
outlines. 

In  bitter  and  sweet  almond,  linseed,  pepo,  and  stropanthus 
are  aleurone  grains. 

In  bitter  and  sweet  almonds  are  stone  cells. 

In  linseed,  quince  seed,  and  in  white  and  black  mustard  are 
epidermal  cells  with  mucilaginous  walls  and  contents,  etc. 


CHAPTER  X 

ARRANGEMENT  OF  VASCULAR  BUNDLES 

Having  familiarized  ourselves  with  the  different  types  of 
mechanical  and  conducting  cells,  we  shall  now  consider  the 
different  ways  in  which  these  cells  are  associated  to  form  the 
vascular  and  fibre-vascular  bundles. 

The  simplest  form  of  the  vascular  bundle  occurs  in  petals, 
floral  bracts,  and  leaves.  In  these  parts  the  vascular  bundle 
is  made  up  of  conducting  cells  only. 

In  the  great  majority  of  cases,  however,  the  conducting  cells 
are  associated  with  mechanical  cells  to  form  the  fibro-vascular 
bundle. 

The  fibre-vascular  bundle  is  made  up  of,  first,  the  phloem, 
which  consists  of  sieve  tubes,  companion  cells,  bast  fibres,  and 
parenchyma;  secondly,  of  the  xylem,  composed  of  vessels  and 
tracheids,  wood  fibres  and  wood  parenchyma;  thirdly,  of  medul- 
lary rays  (restricted  to  certain  types);  and  fourthly,  of  the 
bundle  sheath  (restricted  to  certain  types). 

TYPES   OF  FIBRO-VASCULAR  BUNDLES 

There  are  three  well-defined  types  of  the  fibro-vascular 
bundle,  namely,  the  radial,  the  concentric,  and  the  collateral 
types. 

RADIAL  VASCULAR  BUNDLES 

The  radial  type  of  bundle  is  met  with  most  frequently  in 
monocotyledonous  roots. 

In  this  form  (Plate  114)  the  xylem  forms  radial  bands  of 
tissue  which  alternate  with  isolated  groups  of  phloem.  The 
space  between  the  phloem  and  xylem  is  filled  in  with  either 
parenchyma  or  fibres,  or  both.  In  some  cases  the  vessels  of 
the  xylem  meet  in  the  centre  of  the  root,  while  in  other  cases 

292 


PLATE   124 


CROSS-SECTION  OF  A  RADIAL  VASCULAR  BUNDLE  OF  SKUNK  CABBAGE  ROOT 
(Symplocarpus  foetid  us  [L.],  Nutt.) 

1.  Vessels. 

2.  Bundle  sheath. 

3.  Parenchyma. 

4.  Sieve  cells. 


PLATE   125 


CROSS-SECTION  OF  A  PHLOEM-CENTRIC  BUNDLE  OF  CALAMUS 
RHIZOME  (A  corns  calamus,  L.) 

1.  Vessels. 

2.  Sieve  cells. 

3.  Phloem  parenchyma. 

4.  Parenchyma  surrounding  the  bundles. 


ARRANGEMENT  OF  VASCULAR  BUNDLES  295 

the  centre  of  the  stem  is  occupied  by  pith  parenchyma.  Each 
bundle  is  surrounded  by  parenchyma  cells,  and  in  iris,  calamus, 
and  veratrum,  rhizomes,  and  endodermis,  surrounds  the  bundles 
located  in  the  centre  of  the  stem,  consisting  of  thin-walled 
(mechanical)  ceils. 

In  sarsaparilla  root,  the  pith  is  composed  of  thick-walled, 
porous  pith  parenchyma  cells  with  starch.  Outside  the  pith 
are  arranged  radial  bands  of  oval  vessels  which  decrease  hi  size 
toward  the  periphery.  Between  the  ends  of  these  bands  occur 
isolated  groups  of  sieve  cells. 

Surrounding    the    sieve    cells    and  vessels  are  thick-walled, 
angled  fibres. 

External  to  these  cells  is  an  endodermis  composed  of  lignified 
brownish-colored  cells  one  layer  in  thickness. 

CONCENTRIC   VASCULAR  BUNDLES 

There  are  two  principal  types  of  the  concentric  bundle, 
namely,  xylem-centric,  in  which  the  xylem  is  centric  and  the 
phloem  is  peripheral,  as  in  veratrum  root;  and  phloem-centric 
(Plate  125),  in  which  the  phloem  is  centric  and  the  xylem  pe- 
ripheral, as  in  calamus  rhizome. 

COLLATERAL  VASCULAR  BUNDLES 

There  are  three  types  of  collateral  vascular  bundles — namely, 
closed  collateral,  bi-collateral,  and  open  collateral. 

In  the  closed  collateral  bundle  the  phloem  and  xylem  are 
not  separated  by  a  cambium  layer,  and  in  many  cases  the 
bundle  is  surrounded  by  thick,  angled  walled  fibres,  as  in  palm 
stem.  The  term  closed  bundle  refers  to  the  fact  that  there  is 
no  cambium  between  the  xylem  and  phloem,  therefore  the 
bundle  is  "closed"  to  further  growth,  and  not  to  the  fact  that 
it  is  frequently  surrounded  by  fibres  which  prevent  further 
growth.  In  podophyllum  stem  (Plate  126)  the  xylem  portion 
of  the  bundle  faces  the  centre  of  the  stem  and  the  phloem  portion 
of  the  bundle  faces  the  epidermis.  The  xylem  and  phloem  are 
separated  by  a  cambium  layer,  and  both  are  surrounded  by 
thick-walled  angled  fibres  which  are  the  chief  mechanical  cells 
of  the  stem.  This  bundle  is,  in  fact,  mechanically  closed,  but 
not  physiologically  because  a  cambium  is  present. 


PLATE    126 


CROSS-SECTION  OF  A  CLOSED  COLLATERAL   BUNDLE  OF  MANDRAKE  STEM 
(Podophyllum  peltatum,  L.) 

1.  Vessels. 

2.  Sieve  cells. 

3.  Cambium. 

4.  Fibres. 

5.  Parenchyma. 

6.  Intercellular  space. 


PLATE    127 


Bl-COLLATERAL   BUNDLE   OF  PUMPKIN  STEM    (CurCUrbitd,  pepO,   L.) 

1.  Vessels. 

2.  Sieve  tubes. 


298  HISTOLOGY   OF   MEDICINAL  PLANTS 

BI-COLLATERAL  VASCULAR  BUNDLES 

In  the  bi-collateral  vascular  bundle  (Plate  127)  the  xylem  is 
in  between  two  groups  of  phloem — namely,  an  inner  group  and 
an  outer  group. 

In  pumpkin  stem  a  bundle  occurs  in  each  angle  of  the  stem. 
The  entire  bundle  is  surrounded  by  parenchyma  cells. 

In  an  individual  bundle  the  xylem  consists  of  large  circular 
vessels  and  a  phloem  containing  large  sieve  cells,  many  of 
which  show  the  yellow  porous  sieve  plates. 

OPEN  COLLATERAL  VASCULAR  BUNDLES 

In  the  open  collateral  bundle  (Plate  100)  the  xylem  and 
phloem  are  separated  by  the  cambium  layer,  which,  through 
its  divisions,  causes  the  stem  to  increase  in  thickness  each  year. 
This  type  of  bundle  is  characteristic  of  the  stems  and  roots  of 
dicotyledonous  plants. 

The  bi-collateral  bundle  occurs  in  many  leaves.  The  xylem 
in  such  cases  is  central,  the  phloem  strands  occupying  upper 
and  lower  peripheral  positions. 


INDEX 


Abbe  condenser,  illustration,  1 1 
Absorption  tissue,  introduction,  121 

tissue  of  leaves,  125 
Aerating  tissue,  introduction,  151 
Annular  vessels,  illustration  of,  129 
Bark,   of  white  pine  powdered,   de- 
scription of,  250 

of  white  pine  powdered,  illustra- 
tion of,  251 

unrossed   white   pine,   cross-sec- 
tion, illustration  of,  249 
Barks,  description  of,  248 

diagnostic  structures  of,  253 

structural  variations  of,  252 
Base  sledge  microtome,  35 

sledge  microtome,  illustration,  35 
Bast  fibres,  89 

branched,  92 

branched,  illustrations,  95 

crystal  bearing,  90,  92 

description  of,  100 

groups  of,  illustrations,  102 

non-porous  and  non-striated,  96 

non-porous  and  non-striated,  il- 
lustrations, 101 

non-porous  and  striated,  96 

occurrence   in   powdered   drugs, 
103 

of  barks,  illustrations,  91,  93,  94 

of  klip  buchu  leaf,  262 

of  ruellia  rhizome,  226 

of  ruellia  root,  223 

of  ruellia  stem,  235 

of  spigelia  stem,  235 

porous    and    non-striated,    illus-, 
trations,  98 

porous  and  striated,  92 

porous  and  striated,  illustrations, 

97 

storage  function  of,  179 
striated    and    non-porous,    illus- 
trations of,  99 


Bi-collateral    vascular    bundles,    de- 
scription of,  298 

Buchu  stems,  cross-section,  illustra- 
tion of,  243 

cross-section,  illustration  of,  244 

powdered,  description  of,  245 

powdered,  illustration  of,  246 
Cambium  of  pink  root,  221 

of  ruellia  rhizome,  226 

of  ruellia  stem,  237 

of  spigelia  rhizome,  223 

of  spigelia  stem,  235 
Camera  lucida,  22 

illustrations,  22 
Care  of  microscope,  28 
Celery  fruit,  diagrammatic  drawing  of, 

287 
Cell  contents,  182 

aleurone  grains,  197 

aleurone  grains,   description  of, 
198 

aleurone  grains,  form  of,  197 

aleurone  grains,  structure  of,  197 

aleurone  grains,  tests  for,  198 

chlorophyll,  182 

crystals,  200 

crystals,  composition  of,  200 

crystals,  micro-,  200 

crystals,  raphides,  200 

crystals,  rosette,  200 

crystals,    solitary,    variation   of, 
205 

cystoliths,  210 

cystoliths,  forms  of,  210 

cystoliths,  occurrence  of,  215 

cystoliths,  tests  for,  215 

hesperidin,  196 

hesperdiin,  test  for,  196 

inulin,  194 

inulin,  tests  for,  194 

leucoplastids,  183 

mucilage,  194 


299 


300 


INDEX 


Cell    contents,    mUcilage   associated 

with  raphides,  tests  for,  194 
mucilage,  tests  for,  194 
organic,  182 

starch  grains,  formation  of,  183 
starch  grains,  hilum  nature  of,  188 
starch  grains,  hilum  of,  185 
starch  grains,  mounting  of,  188 
starch  grains,  occurrence  of,  184 
starch  grains,  outline  of,  185 
starch  grains,  size  of,  185 
starch  grains,  tests  for,  188 
tannin,  196 

tannin,  occurrence  of,  196 
tannin,  test  for,  197 
volatile  oil,  test  for,  196 
volatile  oils,  196 

Cell  division  common  to  onion  root, 
56 

Cell  plate,  55 

Cell  sap,  53 

Cell,  typical,  53 

Cell  wall,  53 

Chromatin,  54 

Chromatin  granules,  55 

Chromatophores,  53 

Chromosomes,  55 

Closed  collateral  bundles  of  mandrake 
stem,  cross-section  illustration 
of,  296 

Collateral  vascular  bundles,  295 

Collenchyma    cells,    composition    of 

walls,  109 
illustrations,  108 
occurring  in  catnip  and  mother- 
wort,  illustrations,  107 
of  ruellia  stem,  235 
structure  of,  106 

Compound  microscope,  illustration,  10 
microscope,  mechanical  parts  of, 

7,8 
microscope    of    Robert    Hooke, 

illustration,  8 
microscope,  optical  parts  of,  9, 

II,   12 

microscopes)  introduction,  7 
Concentric  vascular  bundles,  295 
Conducting  tissue,  introduction,  126 
Cork  cells,  origin  of,  88 
Cortical  parenchyma,  conduction  by, 

147 
of  ruellia  stem,  235 


Cortex,  of  pink  root,  219 

of  ruellia  rhizome,  226 

of  ruellia  root,  221 

of  ruellia  stem,  235 

of  spigelia  rhizome,  223 

of  spigelia  stem,  233 
Cover  glasses,  43 

illustrations,  44 
Crystal  cavities,  176 

cells,  storage  function  of,  179 
Cutting  sections,  31 
Cystoliths,  illustrations  of,  214 
Cytoplasm,  53 

Daisies,  white,  powdered,  description 
of,  282 

illustration  of,  283 
Dissecting  microscope,  illustration,  5 

needles,  46 

needles,  illustration,  46 
Drawing  apparatus,  illustration,  23 
Ectoplast,  53 
Embryo,    diagnostic    structures    of, 

291 

Endocarp  of  celery  fruit,  288 
Endodermal     cells,     illustrations    of 
longitudinal  sections,  119 

illustrations  of  cross-sections,  117 

introduction,  116 

structure  of,  116,  118 
Endodermis,    of    klip     buchu    leaf, 
262 

of  pink  root,  219 

of  ruellia  root,  223 
Endosperm  of  celery  fruit,  288 

of  seeds,  291 

Epicarp  of  celery  fruit,  285 
Epidermal    cells    of    leaves,    storage 

function  of,  179 
Epidermis,  surface  deposits  of,  62 

of    herbaceous    steins,    illustra- 
tions of,  152 

of  klip  buchu  leaf,  260 

of  leaves,  illustrations  of,  155 

of  mountain  laurel,  264 

of  pink  root,  219 

of  ruellia  rhizome,  226 

of  ruellia  root,  221 

of  ruellia  stem,  235 

of  seeds,  289 

of  spigelia  rhizome,  223 

of  spigelia  stem,  233 

of  testa,  63 


INDEX 


301 


Epidermis  of  trailing  arbutus,  264 
Equatorial  plane,  55 

plate,  55 
Fibro-vascular  bundles,  composition 

of,  292 

of  klip  buchu  leaf,  262 
types  of,  292 
Flowers,     diagnostic    structures    of, 

284 

parts  of,  270 
Folding  magnifier,  4 

illustration,  4 
Fruits,  cellular  structure  of,  285 

diagnostic      characteristics      of, 

288 

diagnostic  structures  of,  288 
Glandular  hairs  of  peppermint,  178 
illustrations  of,  165 
multicellular,  164 
multicellular,  multiseriate 

stalked,  166 
multicellular,  multiseriate 

stalked,  description  of,  166 
multicellular,  multiseriate 

stalked,  occurrence,  166 
multicellular  sessile,  164 
multicellular  stalked,  164 
multicellular,  uniseriate  stalked, 

164 

stalked,  illustrations  of,  167 
storage  function  of,  178 
unicellular,  164 
unicellular,  multiseriate  stalked, 

164 

unicellular  sessile,  164 
unicellular  stalked,  164 
unicellular,     uniseriate    stalked, 

164 

Glandular  tissue,  introduction,  164 
Glass  slides,  44 

illustrations,  44 
Greenough  binocular  microscope,  15 

illustration,  15 
Guard  cells,  151 

Hairs,     multicellular,      multicellular 

non-branched,  illustration,  75 

multicellular,  multiseriate 

branched,  of  Shepherdia,  78 
multicellular,  multiseriate 

branched,  77,  82 
multicellular,  multiseriate 
branched,  illustrations,  79,  81 


Hairs,  multicellular,  multiseriate  non- 
branched,  74 

multicellular,    uniseriate 
branched,  illustration,  76 

multicellular,    uniseriate    n  o  n  - 
branched,  72 

multicellular,    uniseriate    n  o  n  - 

branched,  illustrations  of,  73 
Hand   cylinder   microtome,   illustra- 
tion, 34 

microtome,  31 

microtome,  illustration,  31 

table  microtome,  34 

table  microtome,  illustration,  34 
Horehound,  powdered,  description  of, 

237 

powdered,  illustration  of,  238 
spurious,   powdered,   description 

of,  237 
spurious,  powdered,  illustration 

of,  239 

Hypoderm  of  seeds,  289 
Hypodermal  cells,  of  leaves,  storage 

function  of,  179 
illustrations,  120 
structure  of,  118 
Hypoderms,  of  klip  buchu  leaf,  260 

of  ruellia  root,  221 
Illumination  for  microscope,  26 
Indirect  cell  division,  54,  55 
Inner  bark  of  white  pine,  248 

epidermis  of  seeds,  291 
Insect  flower  leaves,  powdered,  illus- 
trations of,  268 
stems,  description  of,  241 
stems,  powdered,  illustration  of, 

240 

Insect  flowers,  closed,  powdered,  illus- 
tration of,  279 
open,  description  of,  280 
open,  powdered,  illustration   of, 

281 

powdered,  description  of,  278 
Intercellular  spaces,  158 

illustrations  of,  160,  161 
Internal  phloem,  of  spigelia  stem,  235 
Inulin,  illustrations  of,  195 
Karyokinesis,  54,  55 
Klip  buchu,  cross-section,  illustration 

of,  261 

powdered,  description  of,  262 
powdered,  illustration  of,  263 


302 


INDEX 


Labeling,  47 
Latex  cavities,  176 

tube  cavities,  176 

tubes,  142,  144 

tubes,  illustration  of,  145 

vessels,  illustrations  of,  146 
Leaf  epidermis,  59 

illustrations,  60,  61 
Leaf  parenchyma,  conduction  by,  150 
Leaves,  diagnostic  structures  of,  267 

stomata,  260 
Lenticel,  illustration  of  cross-section, 

159 
Lenticels,  aerating  function  of,  157 

structure  of,  158 
Linin,  54 

Long  paraffin  process,  29 
Machine  microtomes,  32 
Measuring  cylinder,  40 

illustration,  40 
Mechanical  stage,  21 

stage,  illustration,  22 
tissue,  89 

Medullary  ray,  139 
bundle,  139 
bundle   in   tangential-section   of 

quassia  wood,  258 
cell,  141 
cell,  arrangement  of,  in  the  ray, 

142 

cell,  structure  of,  142 
cells,  in  cross-section  of  quassia 

wood,  254 
cells,  in  radial-section  of  quassia 

wood,  258 
cells,     in    tangential-section    of 

quassia  wood,  258 
cells,  of  ruellia  stem,  237 
Medullary  rays,  illustration  of  cross- 
sections  of,  143 

illustration   of  longitudinal   sec- 
tion, 140 
in  cross-section  of  quassia  wood, 

254 
in  radial-section  of  quassia  wood, 

254 

of  pink  root,  221 
of  ruellia  rhizome,  227 
of  ruellia  root,  223 
of  spigelia  rhizome,  226 
of  white  pine  bark,  250 
Mesocarp  of  celery  fruit,  285 


Method  of  mounting  specimens,  41 
Micro-crystals,  illustrations  of,  201 

lamp,  27 
Micrometer  eye-pieces,  21 

illustrations,  20,  21 
Microphotographic  apparatus,  24 

illustration,  24 
Microscope,  how  to  use,  25 
Microscopic  measurements,  19 
Microtome,  care  of,  36 
Middle  bark  of  white  pine,  248 

lamella,  55 

layers  of  seeds,  291 
Minor  rotary  microtome,  36 

illustration,  36 

Mountain  laurel,  cross-section,  illus- 
tration of,  265 
Mucilage  cavities,  172,  176 
Multicellular  hair,  72 
Nuclear  membrane,  55 

spindle,  55 
Nucleoli,  55 
Nucleus,  53 

Objectives,  illustrations,  II 
Ocular  micrometer,  19 

illustration,  19 
Oil  cavities,  occurrence,  178 

of  leaves,  178 

of  seeds,  178 
..     unicellular,  172     - 
Open  collateral  vascular  bundles,  de- 
scription of,  298 

Origin  of  multicellular  plants,  57 
Outer  bark  of  white  pine,  248 
Palisade  parenchyma,  conduction  by, 

150 
Papillae,  67 

illustrations  of,  275 

of  stigmas,  illustrations  of,   276, 
277 

stigma,  description  of,  274 
Paraffin,  blocks,  31 

embedding  oven,  illustration,  30 
Parenchyma,  aquatic  plant,  150 

cells  of  white  pine,  248 

conduction  by,  144 

cortical,  illustrations  of,  148 

of  mountain  laurel,  264 

of  trailing  arbutus,  264 

pith,  illustrations  of,  149 
Pericycle  of  pink  root,  221 

of  ruellia  root,  223 


INDEX 


303 


Periderm,  80 

cork,  80 

illustrations  of,  86 

of  cascara  sagrada,  illustrations, 
84    _ 

of  white  oak  bark,   illustration 
of,  87 

parenchyma  and  stone  cells,  85 

stone  cells,  85 
Permanent  mounts,  41 
Pharmacognostic    microscope,    illus- 
tration, 12 

Phloem,  centric  bundle  of  calamus, 
cross-section,  illustration  of, 
294 

of  ruellia  rhizome,  226 

of  ruellia  stem,  235 

of  spigelia  rhizome,  223 

of  spigelia  stem,  233 
Phloem  parenchyma,  conduction  by, 
150 

of  pink  root,  221 

of  ruellia  rhizome,  226 

of  ruellia  root,  223 

of  ruellia  stem,  235 

of  spigelia  rhizome,  223 

of  spigelia  stem,  235 
Photosynthetic  tissue,  163 
Pink  root,  description  of,  227 
Pith    parenchyma,    conduction     by, 

147 

of  pink  root,  221 

of  ruellia  rhizome,  227 

of  ruellia  root,  223 

of  ruellia  stem,  237 

of  spigelia  rhizome,  226 

of  spigelia  stem,  235 
Pitted  vessels,  with  bordered  pores, 
illustration  of,  135 

illustrations  of,  134 
Plant  hairs,  forms  of,  67 

introduction,  66 
Polar  caps,  55 
Polarization  microscope,  16 

illustration,  16 
Pollen  grains,  270 

non-spiny-walled,  description  of, 
273 

smooth-walled,    illustrations    of, 
271 

spiny-walled,  description  of,  273 

spiny-walled,  illustrations  of,  272 


Preparation  of  specimens  for  cutting, 

28 

Protoplast,  53 

Quassia  wood,  cross-section,  illustra- 
tion of,  255 

radial-section,  illustration  of,  257 
Radial  vascular  bundles,  292 

skunk   cabbage   root,    cross-sec- 
tion, illustration  of,  293 
Raphides,  illustrations  of,  203 
Reading  glass,  4 

illustration,  4 

Reagent  set,  illustration,  39 
Reagents,  list  of,  38 
Research  microscope,  13 

illustration,  14 
Reserve    cellulose,    illustrations    of, 

180-181 

Reticulate  vessels,  illustrations  of,  133 
Root  hairs,  121,  122,  125 

illustration  of,  123 

illustration  of  fragments,  124 
Roots  and  rhizomes,  219 

diagnostic  structures  of,  227 
Rosette  and  solitary  crystals,   illus- 
trations of,  213 

crystals,  illustrations  of,  204 

crystals,  inclosed,  illustrations  of, 

206 

Ruellia    ciliosa,     Pursh.,     powdered, 
illustration  of,  229 

ciliosa,    Pursh.,    rhizome,    cross- 
section,  illustration  of,  225 

ciliosa,    Pursh.,   stem,   cross-sec- 
tion, illustration  of,  236 

root,  description  of,  227 

root,  illustration  of,  222 
Scalpels,  46 

illustration,  47 
Scissors,  46 

illustration,  46 
Sclariform    vessels,    illustrations    of, 

132 

Seeds,  parts  of,  289 
Secretion  cavities,  of  celery  fruit,  288 

description  of,  176 

illustrations  of,  169-171 

introduction,  166 

lysigenous,  168 

schizogenous,  168 

schizo-lysigenous,  168 

unicellular,  168 


304 


INDEX 


Secretion  cells,  of  klip  buchu  leaf,  262 

of  white  pine,  248 
Short  paraffin  process,  29 
Sieve  cells,  of  klip  buchu  leaf,  262 

of  pink  root,  221 

of  ruellia  rhizome,  226 

of  ruellia  root,  223 

of  ruellia  stem,  235 

of  spigelia  stem,  235 
Sieve  plate,  138 

illustration  of,  137 
Sieve  tube,  illustration  of,  137 

tubes,  introduction,  136 

tubes,  structure,  136 
Simple  microscope,  introduction,  3 
Slide  box,  48 

box,  illustration,  48 

cabinet,  49 

cabinet,  illustration  of,  49 

forceps,  45 

forceps,  illustrations,  45 

tray,  48 

tray,  illustration,  48 
Solitary  crystals,  illustrations  of,  207- 

2O9,  211,  212 

unicellular  hairs,  69 
Special  research  microscope,  14 

illustration,  14 

Specimens,  preservation  of,  48 
Spermoderm,  of  celery  fruit,  288 

of  seeds,  289 

Spigelia    marylandica,   powdered,   il- 
lustration of,  228 
rhizome,    cross-section,    illustra- 
tion of,  224 
root,    cross-section,    illustration 

of,  220 
stem,    cross-section,    illustration 

of,  234 

Spindle  fibres,  55 
Spiral    vessels,  illustrations  of,   129, 

130 
Spongy  parenchyma  of  klip  buchu, 

260 
Stage  micrometer,  19 

illustration,  19 
Staining  dish,  40 

illustration,  40 

Standardization    of    ocular    microm- 
eter, 19 

Starch   grains,   illustrations  of,    186, 
187,  189-193 


Steinheil  lens,  5 

illustration,  5 
Stems,  diagnostic  structures  of,  233 

dicotyledonous,  233 

herbaceous,  233 

monocotyledonous,  233 
Stomata,  aerating  function  of,  151 

illustrations  of  cross-section,  156 

relation    to    surrounding    cells, 

154 

types  of,  153 
Stone  cells,  of  ruellia  root,  223 

branched,  109 

branched,  illustrations  of,  no 

description,  in,  112 

introduction,  109 

occurrence,  illustrations,  115 

porous  and  non-striated,  in 

porous   and    non-striated,    illus- 
trations of,  114 

porous  and  striated,  109 

porous  and  striated,  illustrations 
of,  113 

storage  function  of,  178 
Storage  cavities,  176 

cavities,  illustrations  of,  177 

cells,  173 

cells,  cortical  parenchyma,  173 

cells,  illustrations  of,  174 

cells,  pith  parenchyma,  173 

cells,  wood  parenchyma,  173 

tissue,  173 

walls,  description  of,  179 
Stored  mucilage  and  resin,  illustra- 
tions of,  175 
Surrounding    cells,    arrangement    of, 

154 

Synthetic  tissue,  introduction,  163 
Temporary  mounts,  41 
Testa  cells,  65 

epidermal  cells,  illustrations,  64 
Tracheids  of  pink  root,  221 
Trailing   arbutus  leaf,  cross-section, 

illustration  of,  266 
Tripod  magnifier,  4 

illustration,  4 
Turntable,  46 

illustration,  47 
Under  epidermis  of  klip  buchu  leaf, 

262 

epidermis    of    mountain    laurel, 
264 


INDEX 


305 


Under  epidermis  of  trailing  arbutus, 

264 
hypodermis  of   klip   buchu  leaf, 

262 
palisade    parenchyma     of     klip 

buchu  leaf,  262 
Unicellular  clustered  hairs,  72 

clustered  hairs,  illustrations,  71 
non-glandular  hairs,  69 
solitary  branched  hairs,  72 
solitary  hairs,  illustrations,  70 
Upper  palisade  parenchyma  of  klip 

buchu  leaf,  260 

palisade  parenchyma   of   moun- 
tain laurel,  264 
Vacuoles,  53 
Vascular    bundles,    arrangement    of, 

292 

occurrence  of,  292 
Vessels,  annular,  127 

and  tracheids,  introduction,  126 
in  cross-section  of  quassia  wood, 

254 
in  radial-section  of  quassia  wood, 

254 
in  tangential-section  of  quassia 

wood,  258 

of  ruellia  rhizome,  226 
of  ruellia  root,  223 
of  ruellia  stem,  237 
of  spigelia  rhizome,  226 
pitted,  131 

pitted  with  bordered  pores,  131 
reticulate,  131 
sclariform,  128 
spiral,  127 


Water  pores,  aerating  function  of,  151 
Watchmaker's  loupe,  4 

illustration,  4 
Wood  fibres,  color  of,  104 
illustrations,  105 
in  cross-section  of  quassia  wood, 

254 
in  radial-section  of  quassia  wood, 

258 
in  tangential-section  of  quassia 

wood,  258 
introduction,  104 
structure  of,  104 
Wood    parenchyma,   conduction  by, 

150 
in  cross-section  of  quassia  wood, 

254 

in  radial-section  of  quassia  wood, 
258 

of  pink  root,  221 

of  ruellia  rhizome,  227 

of  ruellia  root,  223 

of  ruellia  stem,  237 

of  spigelia  rhizome,  226 

of  spigelia  stem,  235 
Woods,  description  of,  254 

diagnostic  structures  of,  258 
Woody  stems,  buchu  stem,  descrip- 
tion of,  242 

mature  buchu  stem,  242 
Xylem,  of  pink  root,  221 

of  ruellia  rhizome,  226 

of  ruellia  root,  223 

of  ruellia  stem,  237 

of  spigelia  rhizome,  226 

of  spigelia  stem,  235 


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